Simple Interest Calculator
Simple Interest Calculator
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Based on your results — what to do next:
See the full power of compounding
Compounding annually instead of simple interest earns you $76.25 more on $10,000 over 3.0 years — and monthly compounding earns even more.
Put this rate to work for retirement
A 5.00% return compounded over decades — not just 3 years — is how retirement accounts really grow.
Turn this into a savings plan
Earning $1,500.00 in interest on $10,000 — see how adding monthly contributions accelerates any savings goal.
Simple interest is calculated only on the original principal — it never compounds. The formula is I = P × R × T (Principal × Rate × Time). This calculator solves for any one of the four variables — interest earned, principal, rate, or time — and shows how much more you'd earn if the same rate compounded instead.
Simple Interest Formula
Simple interest grows linearly — the same dollar amount of interest accrues every period because it's always calculated on the original principal, never on previously earned interest.
| Variable | Definition |
|---|---|
| I | Interest earned or owed |
| P | Principal — the original amount |
| R | Annual interest rate (decimal, e.g. 5% = 0.05) |
| T | Time in years |
| A | Total amount = Principal + Interest |
Example: $10,000 principal at 5% annual rate for 3 years → I = $10,000 × 0.05 × 3 = $1,500. Total amount A = $11,500. The same $10,000 compounded annually at 5% for 3 years would grow to $11,576 — a modest $76 gap that widens dramatically over longer time horizons.
💡 Expert Pro-Tip
Simple interest favors borrowers; compound interest favors savers. If you're taking out a loan, a simple-interest loan is generally cheaper than an equivalent compound-interest loan, since interest never builds on itself. But if you're saving or investing, you want compounding — ideally as frequently as possible (monthly or daily beats annual). The gap between the two grows with time: over 30 years, compound interest can produce 2–3× more growth than simple interest at the same nominal rate. Always check whether a loan or account quotes a simple or compound (APY) rate before comparing offers.