Finance Tools
Calculators for real money decisions - loans, savings growth, and shopping costs.
These calculators cover the high-value financial questions people search for most: how much will my monthly payment be, how much will my savings grow, and how much will this cost after tax. All calculations run in your browser - nothing is sent anywhere.
About these calculators
Money decisions are rarely about willpower; they're almost always about understanding the numbers before you sign. The three calculators here cover the three financial questions almost everyone runs into at some point: how much will my monthly payment be, how much will my savings grow if I leave them alone, and what's this actually going to cost me at checkout.
The math is the same the bank uses. Knowing it gives you a check on the offer in front of you - and a way to compare two options without trusting either party's spreadsheet.
What each tool answers
- Loan payments. The loan calculator turns a borrowed amount, an interest rate, and a term into a monthly payment using the standard PMT formula. Works identically for mortgages, auto loans, student loans, or personal loans - same math, different numbers.
- Compound growth. The compound interest calculator shows how an investment grows when returns earn returns of their own. The point is not the headline rate but the time horizon - 7% over 30 years quadruples your money; over 10 years it roughly doubles it.
- Sales tax. The sales tax calculator adds tax to a pre-tax price or works backward from a total to recover the pre-tax amount and the tax separately - useful for receipts, expense reports, and quick sanity checks.
Concepts worth getting right
APR vs. APY vs. interest rate. The interest rate is the headline number. APR (Annual Percentage Rate) adds in fees, so it reflects the true cost of borrowing. APY (Annual Percentage Yield) accounts for compounding, so it reflects the true return on saving. Comparing offers using interest rates alone is a near-universal mistake.
Simple vs. compound interest. Simple interest pays you (or charges you) only on the original principal. Compound interest pays on the principal plus accumulated interest. Almost all real-world savings products and loans use compound interest; the difference grows dramatically over long horizons.
Total interest vs. monthly payment. A longer loan term lowers the monthly payment but raises total interest paid, often dramatically. A 15-year mortgage at the same rate can pay roughly half the lifetime interest of a 30-year mortgage on the same loan amount.
Pre-tax vs. post-tax pricing. Many countries display tax-inclusive prices; the US almost always shows pre-tax. When comparing prices internationally or estimating budget, the sales tax calculator removes the guesswork.
Frequently asked questions
Do these calculators include taxes, fees, or insurance?
No. The loan calculator shows principal and interest only. The compound calculator shows pre-tax investment growth. The sales tax calculator handles a single rate. Real bills often include additional line items - add those separately.
What rate should I assume for long-term investing?
Historical global stock-market averages are roughly 5–7% real (after inflation) over very long horizons. For shorter or more conservative scenarios, 3–5% is a safer assumption. Always check the most recent data and your specific account.
Is sales tax or VAT the same everywhere?
No. Rates vary by location. In the US, rates vary by state and city, from 0% to over 10%. Many other countries use VAT set at a national rate. Use the rate that applies to your location.
Why does my actual loan payment differ slightly from the calculator?
Real loans often round to the nearest cent per payment, accrue interest daily on some products, and may roll fees into the principal. Differences are typically small and don't change the overall picture.
Can I model paying extra principal?
Not directly in the loan calculator, but the same effect comes from running it with a shorter term. A 30-year loan paid like a 23-year loan saves a similar amount of interest.