Compound Interest Calculator

How to use it

1. Enter the initial amount (0 is fine if you only make monthly deposits), the annual rate in percent, and the term in whole years.
2. Pick a compounding frequency: yearly, semiannual, quarterly, monthly or daily.
3. Optionally add a monthly contribution; deposits are added at the start of each month, then the balance grows by the effective monthly factor.
4. Read the four headline numbers: final value, total money you put in, interest earned and the effective annual rate.
5. The year-by-year table shows how the balance builds; copy the report to keep the whole schedule.

Common use cases

• Savings planning - see what a fixed monthly deposit grows to over 5, 10 or 30 years.
• Rate comparisons - compare the same nominal rate at different compounding frequencies through the effective annual rate.
• Goal checks - work backwards by trying rates until the final value covers a target.
• Teaching - show how interest on interest separates compound growth from simple interest.

Why it stays private

The simulation runs in this tab with plain arithmetic. Nothing is uploaded, and the tool makes no market or account lookups.

FAQ

Q: When are monthly contributions added? A: At the start of each month, so the first deposit earns a full month of growth. The monthly factor is derived from the nominal rate and frequency as (1 + r/n)^(n/12) - 1, which matches the chosen frequency exactly.

Q: Why does the effective annual rate exceed the nominal rate? A: Compounding reinvests interest during the year. A 6% nominal rate compounded monthly is about 6.17% effective, and the effective column makes that visible.

Q: Is this investment advice? A: No. It is a deterministic estimate. Real returns vary, and taxes, fees and inflation are not included.

Q: How are amounts rounded? A: The initial amount and each monthly deposit are tracked in cents, and interest is rounded half-up for display, so the table never shows phantom sub-cent digits.