Finance Calculators
8 free toolsMortgage, loan, auto loan, compound interest, tip, discount, and sales tax.
Finance calculators show the math behind the number, not just the number: a full amortization schedule with extra payments and the PMI drop date, compound growth with contributions, a car payment with trade-in and tax, and the everyday percent problems of tips, discounts, and reverse sales tax. They are estimates for comparing options, not financial advice, and the assumptions are visible on every page.
Everything here runs in your browser: files and text are processed locally and never uploaded. Nothing you enter is saved.
All 8 tools
Mortgage Calculator
Estimate monthly payments with taxes, insurance, PMI, and a full amortization schedule
Loan Calculator
Monthly payment, total interest, and payoff schedule for any loan
Auto Loan Calculator
Car payment with trade-in, down payment, sales tax, and fees
Compound Interest Calculator
Grow savings with compounding, regular contributions, and a year-by-year table
Tip Calculator
Tip amount, total, and per-person split
Discount Calculator
Sale price from percent off, stacked discounts, and tax
Sales Tax Calculator
Add or back out sales tax from any price
Profit Margin & Markup Calculator
Cost, price, margin, and markup — enter any two and solve the rest
Guides
From the blog: the mechanisms, standards, and edge cases behind these tools.
- Why Your First Mortgage Payment Is Mostly Interest On a $375,000 loan at 7%, payment one is $2,187.50 interest and $307.38 principal. The two-line formula behind it, the crossover month, extra payments, and PMI. Sep 29, 2026 · uses Mortgage Calculator, Loan Calculator, Auto Loan Calculator +1
- Stacked Discounts: Why 20% Off + 10% Off Is 28%, and How to Back Out Sales Tax Discounts multiply, they don't add: 20% then 10% is 28% off. To find the price before tax, divide by 1.08, don't take 8% of the total. Worked examples. Oct 14, 2026 · uses Tip Calculator, Discount Calculator, Sales Tax Calculator
- Margin vs Markup: Why a 50% Markup Is Only a 33% Margin Margin divides profit by price, markup divides it by cost. The conversion table, how to price from a target margin, and why discounts eat margin faster than you think. Oct 13, 2026 · uses Discount Calculator, Sales Tax Calculator, Profit Margin & Markup Calculator
- APR vs APY, and Why Compounding Frequency Matters Less Than You Think APY includes compounding, APR does not, and loan APR adds fees. At 5%, daily beats monthly compounding by about one basis point. Rate and time matter more. Oct 6, 2026 · uses Loan Calculator, Compound Interest Calculator
- Why a Longer Car Loan Costs More (48 vs 60 vs 72 vs 84 Months) Stretching $35,000 from 48 to 84 months cuts the payment by $284.50 but adds $5,982 of interest and years of negative equity. The math, worked out. Oct 6, 2026 · uses Loan Calculator, Auto Loan Calculator
- Coffee to Water Ratio by Brew Method (and Why It's by Weight) The SCA's 55 g per kg of water is about 1:18. Here are the ratio ranges for pour-over, French press, AeroPress, cold brew and espresso, and why grams beat scoops. Sep 30, 2026 · uses Tip Calculator
- Percentage Points vs Percent Change (Same Number, Twice) Percentage points vs percent change: a rate going 10% to 12% is up 2 points and up 20 percent at once. The formulas, the asymmetry trap, reverse percentages. Sep 2, 2026 · uses Profit Margin & Markup Calculator