Simple & Compound Interest Calculator
See how much interest your money earns over time — simple or compound, with an optional regular contribution and a year-by-year growth breakdown.
How to Calculate Interest Earned
- Choose Simple Interest or Compound Interest using the toggle pills.
- Enter your starting amount (principal), annual interest rate, and number of years.
- If using Compound Interest, also choose how often it compounds — annually, semi-annually, quarterly, monthly, or daily — and optionally enter a contribution amount to add at the end of every compounding period.
- Click "Calculate" to see your total interest earned, total contributed, and final balance, plus a year-by-year growth table for Compound Interest.
Frequently Asked Questions
What's the real difference between simple and compound interest?
Simple interest is calculated only on your original principal every year, Final = P × (1 + r × t), so it grows at a constant rate; compound interest is calculated on your principal plus any interest already earned, Final = P × (1 + r/n)^(n×t), so it grows faster over time because you earn interest on interest.
What does the Compounded dropdown actually change?
It sets how many times per year interest is added to your balance — daily compounding yields slightly more than monthly, which yields more than annual, because interest gets added to the balance more frequently and starts earning its own interest sooner.
Which compounding frequency should I pick to match my bank or investment account?
Match whatever your account statement or terms specify — savings accounts commonly compound daily or monthly, while some bonds or fixed-term products compound annually or semi-annually, so check your account disclosures for the exact figure.
Does this calculator account for taxes or fees on interest earned?
No — it shows the raw interest calculation based on the rate, principal, and time you enter, without deducting any taxes, account fees, or withdrawal penalties that might apply to a real account.
How does the optional regular contribution get added?
If you enter an amount in the contribution field, that amount is added to your balance at the end of every compounding period — monthly for Monthly compounding, daily for Daily compounding, and so on — using the standard ordinary-annuity formula. A contribution starts earning interest the period after it's added, not the moment it's deposited.
What does the year-by-year growth table show?
For Compound Interest, it breaks down your balance at the end of each year: how much you've contributed so far, how much interest you've earned so far, and your running total balance — so you can see how much of your growth comes from compounding versus your own deposits.
Is this financial or investment advice?
No — this tool performs a mathematical projection based on a fixed rate you provide; real interest rates on savings, investments, and loans can change over time, so treat the result as an estimate rather than a guarantee or professional recommendation.