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 →Privacy Policy
Last updated: August 14, 2026
Overview
CompelKit ("we", "us", or "our") operates the website at compelkit.com. This Privacy Policy explains how we collect, use, and protect information when you use our free online calculator tools.
Information We Collect
Usage data: We use Google Analytics to collect anonymised information about how visitors interact with our site (pages visited, time on page, device type, general location). This data does not identify you personally.
Calculator inputs: All calculator inputs are processed entirely in your browser. We do not transmit, store, or share any numbers you enter into our calculators on our servers.
Local storage: Your calculator inputs are saved locally in your browser's storage so your data persists between visits. This data never leaves your device.
Account data (if signed in): If you create an account, we store your email address and any profile information you provide, used solely to operate your account.
Cookies & Advertising
Third-party advertising: Third-party vendors, including Google, use cookies to serve ads based on a user's prior visits to this or other websites. Google's use of advertising cookies enables it and its partners to serve ads to users based on their visits to CompelKit and other sites across the web.
Opting out of personalised advertising: You can opt out of Google's personalised advertising by visiting Google Ad Settings, and you can opt out of personalised ads from all participating networks at aboutads.info/choices. These tools let you manage your advertising profile and interest categories across the web.
Analytics cookies: We use Google Analytics cookies to understand anonymised site usage. These cookies collect aggregate, non-identifying data only.
Cookie banner: New visitors are shown a one-time cookie banner on their first visit. The banner lets you accept all cookies — including analytics and personalization — or decline non-essential cookies. Your choice is stored in your browser's local storage so the banner does not reappear. You can clear that choice at any time by clearing local storage for this site, which will cause the banner to reappear on your next visit.
Related Legal Pages
For the legal terms governing use of CompelKit, see our Terms of Service. For the detailed educational-use disclaimer covering our calculators and guides, see our Disclaimer. For how our content is researched, cited, reviewed, and updated, see our Editorial Policy.
How We Use Information
To understand how visitors use CompelKit and improve our tools, to display relevant advertisements via Google AdSense, and to operate and secure user accounts (if applicable).
We do not sell, rent, or share your personal information with third parties for their own marketing purposes.
Third-Party Services
CompelKit uses the following third-party services that may collect data subject to their own privacy policies:
Google Analytics — anonymised site analytics.
Google AdSense — advertising.
Data Retention & Security
Analytics data is retained per Google's standard retention settings. We implement reasonable security measures to protect any account data we hold. Calculator inputs stored in your browser can be cleared at any time by clearing your browser's local storage.
Children's Privacy
CompelKit is not directed at children under 13. We do not knowingly collect personal information from children under 13.
Your Rights
Depending on your location, you may have rights to access, correct, or delete personal data we hold about you. To make a request, contact us via the CompelKit Contact page or the address below.
CCPA Notice (California Residents)
Under the California Consumer Privacy Act (CCPA), California residents have the right to know what personal information we collect, request deletion of it, and opt out of the "sale" or "sharing" of that information. CompelKit does not sell personal information. To exercise your CCPA rights — to know, delete, or opt out — contact us through the CompelKit Contact page. We will verify your request before responding and will not discriminate against you for exercising your rights.
GDPR Notice (EU & UK Residents)
Under the General Data Protection Regulation (GDPR), residents of the European Union and the United Kingdom have rights to access, rectify, erase, restrict, or port their personal data, and to object to certain processing. CompelKit processes only the minimal data described in this policy and relies on legitimate interests (operating and improving the site) and consent (for advertising and analytics cookies) as legal bases. To exercise your GDPR rights, contact us through the CompelKit Contact page. If you are unsatisfied with our response, you may complain to your local data protection authority.
Changes to This Policy
We may update this Privacy Policy from time to time. Changes will be posted on this page with an updated date. Continued use of CompelKit after changes constitutes acceptance of the revised policy.
Contact
If you have questions about this Privacy Policy, please contact us via the CompelKit website.
Privacy Policy
Last updated: August 14, 2026
Overview
CompelKit ("we", "us", or "our") operates the website at compelkit.com. This Privacy Policy explains how we collect, use, and protect information when you use our free online calculator tools.
Information We Collect
Usage data: We use Google Analytics to collect anonymised information about how visitors interact with our site (pages visited, time on page, device type, general location). This data does not identify you personally.
Calculator inputs: All calculator inputs are processed entirely in your browser. We do not transmit, store, or share any numbers you enter into our calculators on our servers.
Local storage: Your calculator inputs are saved locally in your browser's storage so your data persists between visits. This data never leaves your device.
Account data (if signed in): If you create an account, we store your email address and any profile information you provide, used solely to operate your account.
Cookies & Advertising
Third-party advertising: Third-party vendors, including Google, use cookies to serve ads based on a user's prior visits to this or other websites. Google's use of advertising cookies enables it and its partners to serve ads to users based on their visits to CompelKit and other sites across the web.
Opting out of personalised advertising: You can opt out of Google's personalised advertising by visiting Google Ad Settings, and you can opt out of personalised ads from all participating networks at aboutads.info/choices. These tools let you manage your advertising profile and interest categories across the web.
Analytics cookies: We use Google Analytics cookies to understand anonymised site usage. These cookies collect aggregate, non-identifying data only.
Cookie banner: New visitors are shown a one-time cookie banner on their first visit. The banner lets you accept all cookies — including analytics and personalization — or decline non-essential cookies. Your choice is stored in your browser's local storage so the banner does not reappear. You can clear that choice at any time by clearing local storage for this site, which will cause the banner to reappear on your next visit.
Related Legal Pages
For the legal terms governing use of CompelKit, see our Terms of Service. For the detailed educational-use disclaimer covering our calculators and guides, see our Disclaimer. For how our content is researched, cited, reviewed, and updated, see our Editorial Policy.
How We Use Information
To understand how visitors use CompelKit and improve our tools, to display relevant advertisements via Google AdSense, and to operate and secure user accounts (if applicable).
We do not sell, rent, or share your personal information with third parties for their own marketing purposes.
Third-Party Services
CompelKit uses the following third-party services that may collect data subject to their own privacy policies:
Google Analytics — anonymised site analytics.
Google AdSense — advertising.
Data Retention & Security
Analytics data is retained per Google's standard retention settings. We implement reasonable security measures to protect any account data we hold. Calculator inputs stored in your browser can be cleared at any time by clearing your browser's local storage.
Children's Privacy
CompelKit is not directed at children under 13. We do not knowingly collect personal information from children under 13.
Your Rights
Depending on your location, you may have rights to access, correct, or delete personal data we hold about you. To make a request, contact us via the CompelKit Contact page or the address below.
CCPA Notice (California Residents)
Under the California Consumer Privacy Act (CCPA), California residents have the right to know what personal information we collect, request deletion of it, and opt out of the "sale" or "sharing" of that information. CompelKit does not sell personal information. To exercise your CCPA rights — to know, delete, or opt out — contact us through the CompelKit Contact page. We will verify your request before responding and will not discriminate against you for exercising your rights.
GDPR Notice (EU & UK Residents)
Under the General Data Protection Regulation (GDPR), residents of the European Union and the United Kingdom have rights to access, rectify, erase, restrict, or port their personal data, and to object to certain processing. CompelKit processes only the minimal data described in this policy and relies on legitimate interests (operating and improving the site) and consent (for advertising and analytics cookies) as legal bases. To exercise your GDPR rights, contact us through the CompelKit Contact page. If you are unsatisfied with our response, you may complain to your local data protection authority.
Changes to This Policy
We may update this Privacy Policy from time to time. Changes will be posted on this page with an updated date. Continued use of CompelKit after changes constitutes acceptance of the revised policy.
Contact
If you have questions about this Privacy Policy, please contact us via the CompelKit website.