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Interest Calculator
Simple and compound interest on savings or a loan, with deposits, taxes and inflation, and every compounding frequency compared.
Calculated in your browser – nothing you enter is sent or stored.
This interest calculator works out simple interest and compound interest on savings, a deposit or a loan, for any compounding frequency from yearly to daily or continuous. Add monthly deposits, the tax you pay on interest and inflation to see what your money really earns, and compare every interest type side by side.
How to Use the Interest Calculator
- Enter the starting amount, the yearly interest rate and the time in years and months.
- Choose simple interest or how often interest compounds.
- Optionally add a monthly deposit, your tax rate on interest and inflation.
Simple Interest Formula
I = P × r × t – principal × yearly rate × years. Interest is paid only on the original amount. $10,000 at 5% for 10 years earns $10,000 × 0.05 × 10 = $5,000, for a balance of $15,000. Simple interest is used for many car loans, some personal loans and Treasury bills.
Compound Interest Formula
A = P × (1 + r/n)n×t, where n is the number of times interest compounds a year. Interest earns interest, so the balance grows faster. $10,000 at 5% compounded monthly for 10 years becomes $10,000 × (1 + 0.05/12)120 = $16,470.09.
Simple vs Compound: $10,000 at 5% for 10 Years
| Interest type | Ending balance | Interest earned |
|---|---|---|
| Simple interest | $15,000.00 | $5,000.00 |
| Compounded annually | $16,288.95 | $6,288.95 |
| Compounded quarterly | $16,436.19 | $6,436.19 |
| Compounded monthly | $16,470.09 | $6,470.09 |
| Compounded daily | $16,486.65 | $6,486.65 |
| Compounded continuously | $16,487.21 | $6,487.21 |
Compounding adds almost $1,300 over simple interest here. More frequent compounding helps, but the gain from monthly to daily is small – the rate and the time matter far more.
APR vs APY
The APR is the stated yearly rate. The APY (annual percentage yield) includes compounding: 5% compounded monthly is an APY of 5.116%. Banks advertise APY on savings because it is higher; lenders quote APR on loans. Compare savings accounts by APY.
Taxes and Inflation
Interest from savings accounts, CDs and bonds is taxed as ordinary income each year (municipal bond interest is usually exempt from federal tax). If you are in the 22% bracket, a 5% yield keeps only about 3.9% after tax – and if inflation is 3%, your real gain is under 1%. Enter both in the calculator to see your after-tax, inflation-adjusted result.
Sources
- SEC Investor.gov – Compound interest calculator
- FDIC – Truth in Savings Act (Regulation DD) and annual percentage yield
- IRS – Topic no. 403, Interest received
Last reviewed: October 2026 by the ShrinkBee team. Results are estimates for planning and education, not financial, tax, legal or medical advice.
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