Compound Interest Calculator
See how monthly contributions grow over time. Pure client-side, nothing leaves your browser.
Compound interest means each period's earnings get added to the principal, so future periods earn on top of that. Regular contributions (e.g. a fixed monthly deposit) amplify the effect since the principal keeps growing. This tool simulates monthly compounding, matching how most brokerage/401k accounts actually accrue.
Year-by-year
| Year | Contributed | Balance | Growth |
|---|---|---|---|
| 1 | $16,000 | $16,919 | $919 |
| 2 | $22,000 | $24,339 | $2,339 |
| 3 | $28,000 | $32,294 | $4,294 |
| 4 | $34,000 | $40,825 | $6,825 |
| 5 | $40,000 | $49,973 | $9,973 |
| 6 | $46,000 | $59,782 | $13,782 |
| 7 | $52,000 | $70,299 | $18,299 |
| 8 | $58,000 | $81,578 | $23,578 |
| 9 | $64,000 | $93,671 | $29,671 |
| 10 | $70,000 | $106,639 | $36,639 |
| 11 | $76,000 | $120,544 | $44,544 |
| 12 | $82,000 | $135,455 | $53,455 |
| 13 | $88,000 | $151,443 | $63,443 |
| 14 | $94,000 | $168,587 | $74,587 |
| 15 | $100,000 | $186,971 | $86,971 |
| 16 | $106,000 | $206,683 | $100,683 |
| 17 | $112,000 | $227,820 | $115,820 |
| 18 | $118,000 | $250,486 | $132,486 |
| 19 | $124,000 | $274,790 | $150,790 |
| 20 | $130,000 | $300,851 | $170,851 |
FAQ
Is the assumed return rate realistic?
The rate is whatever estimate you type in — this tool gives no investment advice. Historically, US stocks have averaged roughly 7-10% annually including inflation, but past performance doesn't guarantee future results.
Why monthly compounding instead of annual?
Most people contribute monthly (e.g. right after payday), and brokerage accounts typically accrue at least monthly, so this stays closer to how it actually works.
Does this account for taxes or fees?
No — this is a simplified model that ignores capital gains tax, account fees, and other real-world costs, so your actual take-home amount will usually be lower.