Finance Calculators
Compound Interest Calculator
Compound interest is the closest thing to magic in personal finance. Enter a starting amount, rate, and time horizon to see exactly how 'interest on interest' m
Private by design: this tool runs 100% in your browser. Nothing you enter is sent, stored, or tracked.
How to use this calculator
- Enter the starting principal.
- Enter the annual interest rate.
- Enter the number of years.
- Choose compounding frequency (yearly, quarterly, monthly, daily).
- See the future value and interest earned.
The formula
A = P × (1 + r/n)^(n×t), where P is principal, r the annual rate (decimal), n compounding periods per year, and t years.
Worked example
$10,000 at 7% annual interest, compounded monthly for 20 years: A = 10,000 × (1 + 0.07/12)^240 ≈ $40,400 — the interest earned ($30,400) triples the original deposit.
About this tool
Compound interest is the closest thing to magic in personal finance. Enter a starting amount, rate, and time horizon to see exactly how 'interest on interest' multiplies money over the years.
Frequently asked questions
Does compounding frequency matter?
More frequent compounding earns slightly more: monthly beats yearly at the same rate, because interest starts earning interest sooner. Daily vs monthly is a small difference; yearly vs monthly is noticeable over decades.
Simple vs. compound interest?
Simple interest pays only on the original principal. Compound interest pays on principal + accumulated interest — the gap explodes over time.
Is this a prediction of my returns?
No — it's a mathematical illustration using the rate you enter. Real returns vary, and inflation and taxes aren't included.
Does it include monthly contributions?
This version models a single lump sum. Recurring monthly contributions are on the roadmap — they grow even faster.