CompelKit
Precision calculators for your money, your health, and your craft.
Get an instant, accurate answer — no signup, no clutter, no data mining.
Mortgage Calculator
Monthly payments, total interest & amortization breakdown.
CompelKit is a free collection of everyday calculators built for people who just want a quick, accurate answer without creating an account or digging through a cluttered spreadsheet. Whether you're budgeting for a new home, comparing tax structures as a freelancer, or trimming an audio clip for a podcast, each tool on this site is designed to be simple, fast, and precise.
Our Finance tools cover mortgages, property and sales tax, retirement planning, compound interest, and loan payoff strategies — all with exportable reports so you can save or share your results. Our Lifestyle tools help with everyday tasks like splitting a bill, counting calories, or converting units. And our Creative tools give podcasters, voiceover artists, and audio editors a way to time scripts, optimize bitrates, and edit audio directly in the browser.
Featured Guides
All guidesThe Freelancer's Tax Survival Guide: LLC vs. Sole Proprietorship
A practical, in-depth breakdown of how sole proprietorships and S-Corp LLCs are taxed differently — and exactly when switching structures actually saves you money.
FinanceCompound Interest: The Quiet Multiplier of Wealth
Why time — not timing — is the single biggest variable in long-term investing, and how to use compounding math to your advantage no matter your starting point.
CreativeAudio Bitrate Explained: Finding the Sweet Spot for Quality and Size
A practical, no-nonsense guide to what bitrate actually measures, how it affects perceived audio quality, and exactly which settings to use for podcasts, music, and archival masters.
Favourites
Finance
Mortgage Calculator
Monthly payments, total interest & amortization breakdown.
Sales Tax & Margin
Reverse sales tax, profit margins & markup calculations.
Property Tax & Affordability
Estimate property taxes & how much home you can afford.
Freelance Tax & LLC Savings
Compare sole proprietor vs LLC tax obligations.
Budget Planner
Plan and track home & business monthly budgets with exports.
Currency Converter
Real-time exchange rates & multi-currency comparisons.
Retirement Calculator
Plan retirement with income strategies, withdrawal projections & sustainability analysis.
Compound Interest
Grow any investment with compound interest & regular contributions.
Loan Payoff Calculator
See payoff timelines & interest saved with extra payments.
Hourly to Salary
Convert hourly wages to annual salary and back, instantly.
Lifestyle
Calorie Counter
Calculate your daily calorie target & log meals with macros.
Tip & Bill Splitter
Split any bill with custom tip percentages across your party.
Unit Converter
Convert length, weight, temperature, volume, speed, area & data.
Square Footage Calculator
Calculate total square footage across rooms & estimate material cost.
TDEE Calculator
Calculate your Total Daily Energy Expenditure & BMR.
Drywall Calculator
Visual panel, joint compound & screw estimator for any room.
Brick Calculator
Estimate bricks & mortar bags for any wall, visually.
Gravel Calculator
Estimate volume, weight & cost for gravel, stone, or sand fill.
Lumber Calculator
Calculate board footage for any lumber order.
Decking Calculator
Estimate deck boards & fasteners, visually.
Framing Calculator
Estimate wall studs & plate lumber, visually.
Tile Calculator
Estimate tiles needed for any room, visually.
Creative
Script Timer
Estimate read time for TTS & voiceover scripts.
Audio Bitrate Optimizer
Calculate file sizes & optimal bitrates for audio.
Audio Editor
Trim, adjust volume & export audio to MP3, WAV, OGG, AAC or FLAC.
Batch Processor
Process multiple audio files at once with the same effect & download as ZIP.
Mortgage Calculator
Calculate monthly payments, total interest, and loan breakdown.
Auto-fill Tax & Insurance by Zip Code
Payment Breakdown
Annual Payment Split
Remaining Loan Balance Over Time
Cumulative Interest Paid vs. Principal Recovered
Early in the loan, most payments go to interest — see when the balance shifts
💡 Principal recovered exceeds cumulative interest at Year 0 — before this point, most of your payments fund interest.
Loan Term Comparison
15 vs 20 vs 30-year breakdown at 6.5% · $280,000 loan
| Term | Monthly Payment | Total Interest | Total Paid | vs 30yr Interest |
|---|---|---|---|---|
| 15-year | $2,439.10 | $159,038 | $439,038 | −$198,086 |
| 20-year | $2,087.60 | $221,025 | $501,025 | −$136,099 |
| 30-year | $1,769.79 | $357,125 | $637,125 | baseline |
15-Year Term
20-Year Term
30-Year Term
How This Calculator Works
A mortgage is an amortizing loan used to buy a home, repaid in fixed monthly installments across a set term (commonly 15 or 30 years). Each payment splits into two parts: principal, the borrowed amount you are paying back, and interest, the lender's fee calculated on the remaining balance. Because interest is charged on the outstanding balance, early payments are interest-heavy — a pattern called front-loaded amortization. Your down payment reduces the loan size; a 20% down payment also avoids Private Mortgage Insurance (PMI). Adding extra principal each month reduces the balance faster, which shrinks future interest and shortens the term. The PITI figure combines principal and interest with property tax and homeowners insurance to show your true monthly housing cost, which is what lenders use when qualifying you against a debt-to-income ratio.
The Mathematical Formula & Logic
The standard amortization formula for the fixed monthly principal-and-interest payment is M = P × [ r(1 + r)ⁿ ] / [ (1 + r)ⁿ − 1 ]. P is the loan principal (home price minus down payment). r is the monthly interest rate (annual rate ÷ 12, expressed as a decimal). n is the total number of monthly payments (loan term in years × 12). Total interest paid over the loan equals (M × n) − P. Each month the remaining balance updates as B_new = B_old × (1 + r) − M.
Worked Step-by-Step Example
Consider a $350,000 home with a 20% down payment on a 30-year fixed loan at 6.5% interest. The down payment is $70,000, so the loan principal P = $280,000. The monthly rate r = 0.065 ÷ 12 = 0.0054167, and n = 360 payments. Plugging into the formula gives a monthly P&I payment of about $1,771.66. Over 360 months you pay $637,798 total, of which $357,798 is interest. Adding a $200/month extra principal payment reduces total interest by roughly $97,000 and pays the loan off about 6 years early.
Frequently Asked Questions
Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.
Read the full guide: How Mortgage Amortization Really Works →Audio Editor
Trim, adjust and export using the menu bar above
Drop an audio file here
or click to browse — MP3, WAV, OGG, FLAC, AAC, M4A
Tip: use File menu or drag a file to get started
How to use the Audio Editor
- Load audio via the drop zone above, File → Open, Load from URL, or record directly from your microphone.
- Drag the Trim Start / Trim End sliders to select the section you want to keep.
- Adjust Volume, or open the Effects menu for gain, fades, EQ, noise reduction, and more.
- Use Edit → Undo/Redo at any point to step back through your changes.
- Export your result from the Quick Export buttons or File → Export as MP3, WAV, OGG, AAC, or FLAC.
Everything runs locally in your browser — no files are uploaded to a server.
How This Calculator Works
The CompelKit audio editor runs entirely in your browser using ffmpeg.wasm, so your files are never uploaded to a server. You can load an audio file, trim it to a region, apply effects (fade, normalize, speed, volume, EQ), and export to MP3, WAV, OGG, AAC, or FLAC. Editing is non-destructive: trims and effect settings are stored as parameters and applied during export, so you can adjust and re-export without quality loss from repeated re-encoding of the source. Multitrack mixing lets you layer two clips and balance their levels before export.
The Mathematical Formula & Logic
Trim region is encoded as a start time and end time (in seconds).
Export pipeline = ffmpeg filter chain applied to the source: trim → effects (fade, volume, atempo) → encoder (libmp3lame, pcm_s16le, libvorbis, aac, flac). Output file size follows the bitrate formula: (Bitrate × Duration) / 8 / 1024 MB.
Worked Step-by-Step Example
Trim a 3:00 clip to the first 2:30 by setting the end marker to 2 minutes 30 seconds, then export to MP3 at 128 kbps. The exported file is 2:30 long and about (128 × 150) / 8 / 1024 ≈ 2.34 MB — no upload, no server round-trip, the entire operation runs locally in your browser.
Frequently Asked Questions
Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.
Read the full guide: A Browser-Based Audio Editor Explained →Currency Converter
Real-time exchange rates powered by Frankfurter (ECB data)
Could not load exchange rates. Check your connection and try again.
How This Calculator Works
Currency conversion multiplies an amount in one currency by the exchange rate to express it in another. Exchange rates fluctuate continuously based on supply and demand in foreign-exchange markets, central bank policy, interest rates, and trade flows. This tool pulls live mid-market rates so the result reflects the current wholesale rate; the rate a consumer actually receives at a bank or kiosk adds a margin (a spread), so the amount you convert at the airport is usually worse than the mid-market figure shown here. Use the comparison view to see several currencies at once and the historical chart to gauge whether a rate is favorable relative to the recent past.
The Mathematical Formula & Logic
Converted Amount = Amount × Rate (units of target currency per one unit of source currency). To invert: Rate_inverse = 1 ÷ Rate. A percentage change over time = ((Rate_now − Rate_then) ÷ Rate_then) × 100.
Worked Step-by-Step Example
Converting $1,000 USD to EUR at a rate of 0.92 euros per dollar gives 1,000 × 0.92 = €920. If the rate a week earlier was 0.90, the dollar strengthened by ((0.92 − 0.90) ÷ 0.90) × 100 ≈ 2.22%, meaning your $1,000 buys about €20 more than it did last week. A bank charging a 3% margin would give you only about €892 instead of the €920 mid-market figure.
Frequently Asked Questions
Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.
Read the full guide: How Currency Exchange Rates Actually Work →Budget Planner
Plan and track your monthly income and expenses.
Expense Categories
| Category | Budgeted | Actual | Diff | |
|---|---|---|---|---|
| +$1,500.00 | ||||
| +$200.00 | ||||
| +$400.00 | ||||
| +$300.00 | ||||
| +$250.00 | ||||
| +$150.00 | ||||
| +$200.00 | ||||
| +$500.00 | ||||
| +$100.00 | ||||
| +$100.00 | ||||
| Totals | $3,700.00 | $0.00 |
💡 Home Budget Tips
- • Follow the 50/30/20 rule (needs/wants/savings)
- • Track your spending for the first month
- • Build an emergency fund first
- • Review subscriptions and cancel unused ones
- • Meal plan to reduce grocery costs
- • Automate your savings contributions
How This Calculator Works
A budget divides income into planned categories so you can see where money goes and adjust before overspending. This planner supports two templates: a personal (home) budget using the 50/30/20 framework (needs, wants, savings) and a business budget that separates cost of goods, operating expenses, and owner compensation with a tax reserve. Each category is editable, with subtotals for income and expenses and a net surplus or deficit that updates live. The business tab also estimates a quarterly tax reserve so owners set aside funds as they earn rather than scrambling at filing time.
The Mathematical Formula & Logic
Net = Total Income − Total Expenses. For the home budget, target allocation = Income × percentage (50% needs, 30% wants, 20% savings/debt). For the business budget: Net Operating Income = Revenue − COGS − Operating Expenses; Owner Draw = Net Operating Income − Tax Reserve; Tax Reserve = Taxable Income × estimated effective rate ÷ 4 per quarter.
Worked Step-by-Step Example
On $5,000 monthly take-home, the 50/30/20 split allocates $2,500 to needs, $1,500 to wants, and $1,000 to savings or debt payoff. A business with $8,000 monthly revenue, $2,500 COGS, and $3,000 operating expenses has $2,500 in net operating income; setting aside 25% for taxes ($625/month) leaves $1,875 for owner draw and reinvestment — tracked across the full year to avoid a tax surprise.
Frequently Asked Questions
Disclaimer: CompelKit tools and calculators are provided for educational and estimation purposes only and do not constitute certified legal, financial, or tax advice.
Read the full guide: Budgeting Frameworks That Actually Work →Terms of Service
Last updated: August 11, 2026
1. Acceptance of These Terms
By accessing or using CompelKit ("the Site," "we," "our," or "us"), you agree to be bound by these Terms of Service ("Terms"). If you do not agree, please discontinue use of the Site. These Terms apply to all visitors — registered and unregistered — and to every tool and guide on the Site.
2. Nature of CompelKit
CompelKit provides free, browser-based calculators and educational guides across finance, construction, lifestyle, and audio topics. Every tool, output, chart, and article on this Site is offered as an educational resource — not as financial, tax, legal, building-code, or medical advice of any kind. See our Disclaimer page for the full statements that govern the use of every calculator.
3. License to Use the Site
CompelKit grants you a personal, non-exclusive, non-transferable, revocable license to access and use the Site for your own non-commercial, informational, and educational purposes. You may not: (a) resell, sublicense, or re-distribute our calculators or content as a paid product; (b) scrape, mirror, or copy the Site's text, calculations, or charts to another domain without express written permission; (c) use automated scripts to overload or disrupt the Site; or (d) attempt to extract user data, bypass our advertising controls, or interfere with any third-party integrations.
4. Calculator Accuracy & Limitations
While every calculator is built using widely accepted formulas (standard amortization math, published federal tax brackets, BMR/TDEE equations, board-foot lumber formulas, and similar public-domain methods), each tool relies on values you enter and the assumptions explained in that tool's guide. Results are estimates and may not reflect your individual tax situation, local building codes, lender requirements, or jurisdiction-specific rules. Tax law, lending requirements, and material standards change frequently; CompelKit does not guarantee that any figure shown is current, complete, or applicable to you. Always verify critical figures against your loan statement, tax preparer, supplier invoice, or other authoritative source before acting on a calculator result.
5. User Accounts and Inputs
Where the Site supports optional user accounts (for projects, saved snapshots, or history), you are responsible for safeguarding your credentials and for any activity under your account. All calculator inputs are processed in your browser; we do not store the numbers you enter on our servers. CompelKit is not responsible for any loss you may incur from sharing your credentials or failing to log out on shared devices.
You agree not to submit content via the Contact form, tool suggestions, or project notes that is unlawful, defamatory, infringes others' intellectual property, or contains malware or harmful code. We may delete any submission we believe violates these Terms without notice.
6. Third-Party Links, AdSense, and Affiliate Disclosure
The Site may display advertisements served by Google AdSense and may link to third-party websites for reference and citation. We are not responsible for the content, accuracy, or practices of any third-party site and accept no liability for any loss or damage arising from your reliance on external websites. We may earn advertising revenue from ads shown on the Site. Where any article or guide links to a product or service for which we receive compensation, that relationship will be disclosed at the point of the link.
7. Intellectual Property
All original content on this Site — including calculator logic, written guides, the "CompelKit" name and logo, layout, and design — is the property of CompelKit and protected by applicable copyright and trademark laws. External data referenced in our citation boxes belongs to its respective owners (IRS, CFPB, BLS, HUD, etc.) and is used here solely for educational reference.
8. Disclaimer of Warranties
The Site and all content are provided "AS IS" without warranties of any kind, express or implied, including implied warranties of merchantability, fitness for a particular purpose, or non-infringement. We do not warrant that the Site will be uninterrupted, error-free, malware-free, or that any calculator output is accurate, complete, or applicable to your circumstances. See our Disclaimerpage for additional limits on liability.
9. Limitation of Liability
To the maximum extent permitted by applicable law, CompelKit, its operators, contributors, and affiliates shall not be liable for any direct, indirect, incidental, consequential, special, or exemplary damages arising from your use of — or inability to use — the Site, including but not limited to financial losses resulting from decisions made on the basis of calculator output. Your use is entirely at your own risk.
10. Changes to These Terms
We may revise these Terms from time to time. The updated date at the top of this page reflects the most recent revision. Continued use of the Site after changes constitutes acceptance of the updated Terms.
11. Governing Law
These Terms shall be governed by and construed in accordance with the laws of the United States and the state in which the Site is operated, without regard to conflict-of-law principles. Any disputes shall be submitted to the exclusive jurisdiction of the competent courts in that state.
12. Contact
Questions about these Terms, requests for permission to reuse content, or notices of suspected violation may be sent via our Contact page.
Terms of Service
Last updated: August 11, 2026
1. Acceptance of These Terms
By accessing or using CompelKit ("the Site," "we," "our," or "us"), you agree to be bound by these Terms of Service ("Terms"). If you do not agree, please discontinue use of the Site. These Terms apply to all visitors — registered and unregistered — and to every tool and guide on the Site.
2. Nature of CompelKit
CompelKit provides free, browser-based calculators and educational guides across finance, construction, lifestyle, and audio topics. Every tool, output, chart, and article on this Site is offered as an educational resource — not as financial, tax, legal, building-code, or medical advice of any kind. See our Disclaimer page for the full statements that govern the use of every calculator.
3. License to Use the Site
CompelKit grants you a personal, non-exclusive, non-transferable, revocable license to access and use the Site for your own non-commercial, informational, and educational purposes. You may not: (a) resell, sublicense, or re-distribute our calculators or content as a paid product; (b) scrape, mirror, or copy the Site's text, calculations, or charts to another domain without express written permission; (c) use automated scripts to overload or disrupt the Site; or (d) attempt to extract user data, bypass our advertising controls, or interfere with any third-party integrations.
4. Calculator Accuracy & Limitations
While every calculator is built using widely accepted formulas (standard amortization math, published federal tax brackets, BMR/TDEE equations, board-foot lumber formulas, and similar public-domain methods), each tool relies on values you enter and the assumptions explained in that tool's guide. Results are estimates and may not reflect your individual tax situation, local building codes, lender requirements, or jurisdiction-specific rules. Tax law, lending requirements, and material standards change frequently; CompelKit does not guarantee that any figure shown is current, complete, or applicable to you. Always verify critical figures against your loan statement, tax preparer, supplier invoice, or other authoritative source before acting on a calculator result.
5. User Accounts and Inputs
Where the Site supports optional user accounts (for projects, saved snapshots, or history), you are responsible for safeguarding your credentials and for any activity under your account. All calculator inputs are processed in your browser; we do not store the numbers you enter on our servers. CompelKit is not responsible for any loss you may incur from sharing your credentials or failing to log out on shared devices.
You agree not to submit content via the Contact form, tool suggestions, or project notes that is unlawful, defamatory, infringes others' intellectual property, or contains malware or harmful code. We may delete any submission we believe violates these Terms without notice.
6. Third-Party Links, AdSense, and Affiliate Disclosure
The Site may display advertisements served by Google AdSense and may link to third-party websites for reference and citation. We are not responsible for the content, accuracy, or practices of any third-party site and accept no liability for any loss or damage arising from your reliance on external websites. We may earn advertising revenue from ads shown on the Site. Where any article or guide links to a product or service for which we receive compensation, that relationship will be disclosed at the point of the link.
7. Intellectual Property
All original content on this Site — including calculator logic, written guides, the "CompelKit" name and logo, layout, and design — is the property of CompelKit and protected by applicable copyright and trademark laws. External data referenced in our citation boxes belongs to its respective owners (IRS, CFPB, BLS, HUD, etc.) and is used here solely for educational reference.
8. Disclaimer of Warranties
The Site and all content are provided "AS IS" without warranties of any kind, express or implied, including implied warranties of merchantability, fitness for a particular purpose, or non-infringement. We do not warrant that the Site will be uninterrupted, error-free, malware-free, or that any calculator output is accurate, complete, or applicable to your circumstances. See our Disclaimerpage for additional limits on liability.
9. Limitation of Liability
To the maximum extent permitted by applicable law, CompelKit, its operators, contributors, and affiliates shall not be liable for any direct, indirect, incidental, consequential, special, or exemplary damages arising from your use of — or inability to use — the Site, including but not limited to financial losses resulting from decisions made on the basis of calculator output. Your use is entirely at your own risk.
10. Changes to These Terms
We may revise these Terms from time to time. The updated date at the top of this page reflects the most recent revision. Continued use of the Site after changes constitutes acceptance of the updated Terms.
11. Governing Law
These Terms shall be governed by and construed in accordance with the laws of the United States and the state in which the Site is operated, without regard to conflict-of-law principles. Any disputes shall be submitted to the exclusive jurisdiction of the competent courts in that state.
12. Contact
Questions about these Terms, requests for permission to reuse content, or notices of suspected violation may be sent via our Contact page.