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.
CreativeBrowser Audio Editing Explained: Trim, Effects & Export Without Uploads
How a browser-based audio editor powered by ffmpeg.wasm can trim, normalize, EQ, and export your recordings entirely on-device — and the privacy and trade-offs that come with it.
FinanceHow Mortgage Amortization Really Works (And How to Beat It)
Why your early mortgage payments barely touch the principal, and the exact strategies that shift the math in your favor — from extra payments to refinancing timing.
FinanceBudgeting Frameworks That Actually Work (Home & Business)
The 50/30/20 rule, zero-based budgeting, and the tax-reserve discipline every small business needs — a practical comparison of proven budgeting systems.
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
P&I is just principal and interest. PITI adds property taxes and homeowners insurance to show your full monthly housing cost. Lenders qualify you on PITI when measuring debt-to-income, not on P&I alone.
Every extra dollar above your scheduled payment reduces principal directly. Because interest is charged on the remaining balance, a lower principal means less interest accrues each month — a compounding saving that also shortens the loan term.
PMI is required below a 20% down payment. By law it is automatically canceled at 78% loan-to-value, and you can request removal at 80% LTV with a good payment history. Extra principal payments help you reach that threshold sooner.
Refinancing pays off when the interest savings offset closing costs (typically 2–5% of the loan). A common rule is to refinance when rates drop at least 1% below your current rate and you will stay in the home past the break-even point shown in the Refinance tab.
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
Yes. All processing uses ffmpeg.wasm compiled to WebAssembly and runs locally in your browser tab. Your audio files are never uploaded to a server, so they stay on your device throughout editing and export.
Import supports MP3, WAV, FLAC, AAC, M4A, OGG, Opus, AIFF, and more. Export to MP3, WAV, OGG, AAC, or FLAC. WAV and FLAC are lossless; MP3, OGG, and AAC are compressed and let you choose a bitrate to balance quality and size.
No. Trims are stored as a region (start and end time) and applied once during export, so the source buffer isn't re-encoded until the final export. Repeated adjustments and re-exports don't compound quality loss the way repeatedly re-saving a lossy file would.
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
The mid-market rate is the midpoint between buy and sell prices on global currency markets — the true wholesale rate. Retail providers add a spread on top, so consumers rarely receive exactly this rate.
Rates move with supply and demand, driven by interest rates, inflation, trade balances, central bank policy, and geopolitical events. Higher local interest rates usually strengthen a currency.
No one can time the market reliably, but checking a historical chart helps you see if today's rate is high or low relative to the recent range. For large conversions, avoid airport kiosks with wide spreads.
Providers charge either a fixed fee, a percentage spread, or both. The spread is the difference between the rate you get and the mid-market rate — often the largest hidden cost of converting money.
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
50% of income to needs (housing, food, utilities), 30% to wants, and 20% to savings or debt payoff. It is a flexible starting point, not a strict rule — adjust the splits to fit your goals.
Zero-based budgeting assigns every dollar a job so income minus expenses equals exactly zero. It forces intentional spending and is more precise than defaulting leftover money to 'savings.'
Self-employment income usually has no withholding, so setting aside a percentage each month prevents a cash crunch at filing time. Many owners target 25–30% of profit as a safe reserve.
Review monthly and re-baseline quarterly. A monthly check catches overspending early; a quarterly reset adjusts categories based on what actually happened and changed goals.
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 →Construction & Material Guides
CompelKit's construction guides turn the takeoff math behind a building project into something you can actually follow. Whether you are estimating drywall panels for a bedroom, board feet for a lumber order, or the number of tiles and boxes a room requires, each guide explains the formula, the waste buffer that separates a clean order from a mid-project shortage, and the common mistakes that make DIYers order too little or too much.
Every guide is tied to a free calculator that applies the math to your exact dimensions — room size, panel dimensions, stud spacing, or gravel depth — with a live visual diagram that updates as you type. The articles cite the standards behind the numbers, from nominal lumber sizes to industry mortar ratios, so you can order with confidence and know why the result is what it is.
Guides
Drywall Estimating: How to Calculate Panels, Compound, and Screws
A practical walkthrough of drywall takeoff math — from wall area and panel count to the joint compound, tape, and screws that complete the job — so you order right the first time.
Tile Layout Math: How to Calculate Tiles Needed (and Buy Enough)
From room area and tile dimensions to the waste buffer that varies by pattern, this guide explains how to turn a floor or wall into an exact tile count — and why running short is the most expensive mistake in tiling.
Lumber Takeoff: How to Calculate Board Feet and Order Right
Board footage, nominal vs. actual dimensions, and the waste buffer that keeps a framing or woodworking project from stalling — the complete guide to ordering lumber accurately.
Framing Math: How to Calculate Studs and Plate Lumber for a Wall
The 16-inch on-center rule, the studs hidden at corners and openings, and the plate lumber every wall needs — a clear breakdown of wall framing takeoff math.
Decking Calculator Guide: How Many Boards and Screws You Really Need
Deck area, board coverage, waste by layout pattern, and fastener counts — everything that goes into an accurate decking material order, including the gap that changes the math.
How to Measure Square Footage for Any Room or Project
The foundation of every material estimate — from flooring to paint to tile — is accurate square footage. This guide explains how to measure simple and irregular rooms and how the waste buffer turns area into an order quantity.
Gravel and Fill Material: How to Order by Volume, Weight, and Cost
Loose-fill materials are measured by volume but sold by weight. This guide explains how to convert between cubic feet, cubic yards, and tons — and why the compaction buffer keeps a driveway from sinking.
Calculators
Square Footage Calculator
Calculate total square footage across rooms & estimate material cost.
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.
Construction & Material Guides
CompelKit's construction guides turn the takeoff math behind a building project into something you can actually follow. Whether you are estimating drywall panels for a bedroom, board feet for a lumber order, or the number of tiles and boxes a room requires, each guide explains the formula, the waste buffer that separates a clean order from a mid-project shortage, and the common mistakes that make DIYers order too little or too much.
Every guide is tied to a free calculator that applies the math to your exact dimensions — room size, panel dimensions, stud spacing, or gravel depth — with a live visual diagram that updates as you type. The articles cite the standards behind the numbers, from nominal lumber sizes to industry mortar ratios, so you can order with confidence and know why the result is what it is.
Guides
Drywall Estimating: How to Calculate Panels, Compound, and Screws
A practical walkthrough of drywall takeoff math — from wall area and panel count to the joint compound, tape, and screws that complete the job — so you order right the first time.
Tile Layout Math: How to Calculate Tiles Needed (and Buy Enough)
From room area and tile dimensions to the waste buffer that varies by pattern, this guide explains how to turn a floor or wall into an exact tile count — and why running short is the most expensive mistake in tiling.
Lumber Takeoff: How to Calculate Board Feet and Order Right
Board footage, nominal vs. actual dimensions, and the waste buffer that keeps a framing or woodworking project from stalling — the complete guide to ordering lumber accurately.
Framing Math: How to Calculate Studs and Plate Lumber for a Wall
The 16-inch on-center rule, the studs hidden at corners and openings, and the plate lumber every wall needs — a clear breakdown of wall framing takeoff math.
Decking Calculator Guide: How Many Boards and Screws You Really Need
Deck area, board coverage, waste by layout pattern, and fastener counts — everything that goes into an accurate decking material order, including the gap that changes the math.
How to Measure Square Footage for Any Room or Project
The foundation of every material estimate — from flooring to paint to tile — is accurate square footage. This guide explains how to measure simple and irregular rooms and how the waste buffer turns area into an order quantity.
Gravel and Fill Material: How to Order by Volume, Weight, and Cost
Loose-fill materials are measured by volume but sold by weight. This guide explains how to convert between cubic feet, cubic yards, and tons — and why the compaction buffer keeps a driveway from sinking.
Calculators
Square Footage Calculator
Calculate total square footage across rooms & estimate material cost.
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.