No. 003 — Finance
Compound Interest Calculator
Project how a starting balance and monthly contributions grow over time.
How this calculator works
Each compounding period, this tool adds interest on your current balance, then adds your monthly contribution before the next period compounds — so your contributions also start earning interest right away. Choosing a more frequent compounding schedule (daily vs. annually) makes a small but real difference over long time horizons, since interest is calculated and added back more often.
Frequently asked
- What's the difference between compound and simple interest?
- Simple interest is only ever calculated on your original balance. Compound interest is recalculated on your balance plus all previously earned interest, so growth accelerates over time.
- Does compounding frequency matter much?
- It matters more as your time horizon grows. Over 20-30 years, monthly or daily compounding will noticeably outperform annual compounding at the same stated rate.