Interest Calculator
Last updated: June 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
Quick reference
| Type | Formula |
|---|---|
| Simple interest | I = P × r × t |
| Annual compound | A = P(1+r)^t |
| Monthly compound | A = P(1+r/12)^(12t) |
savings Plan with confidence
Finance decisions get a lot easier when you can see the full picture. Enter your numbers above to see total payments, interest paid, and the long-term cost of every choice — so you can compare options side by side before signing anything.
percent How the math works
We use the standard amortization, compound-interest and present-value formulas published by the Consumer Financial Protection Bureau and the Federal Reserve. The methodology block below shows every variable and rounding step we apply, so the answer is never a black box.
shield_lock Your data stays private
Every calculation happens in your browser with JavaScript — your income, balances, and loan numbers are never sent to our servers, logged, or shared. Close the tab and the inputs vanish. No sign-up, no tracking pixels on the form, no spreadsheet emailed to you later.
lightbulb Pro tip
Save the URL after you calculate — your inputs aren't stored, so write down the headline number plus the breakdown. Then come back and edit one variable at a time (down payment, rate, term) to see exactly which lever moves your monthly figure the most. That's where the real planning happens.
Interpretation guide
| Use case | Best metric |
|---|---|
| Loans | Total interest paid |
| Savings | Future balance |
| Compare rates | Use APY/EAR when compounding differs |
lightbulb Example — simple interest on $2,000 at 5% for 3 years
Result: Interest = $300; total = $2,300.
What this means: Simple interest is linear; with compound interest the total would be slightly higher because interest earns interest.
Formula & methodology
Formula: Simple: I = PRT; compound: A = P(1+r/n)^(nt)
Simple interest pays only on principal. Compound interest pays on principal plus previously earned interest, so compounding frequency changes the effective return.