Compound Interest Calculator
Project how a lump sum or regular contributions grow over time with compound interest — see your final balance, total contributions, and total interest earned.
Final balance
$144,572.72
Total contributions
$48,000
Total interest earned
$86,573
Show year-by-year growth
| Year | Contributions | Interest Earned | Balance |
|---|---|---|---|
| Year 1 | $2,400.00 | $801.42 | $13,201.42 |
| Year 2 | $2,400.00 | $1,032.85 | $16,634.27 |
| Year 3 | $2,400.00 | $1,281.01 | $20,315.28 |
| Year 4 | $2,400.00 | $1,547.11 | $24,262.39 |
| Year 5 | $2,400.00 | $1,832.45 | $28,494.83 |
| Year 6 | $2,400.00 | $2,138.41 | $33,033.24 |
| Year 7 | $2,400.00 | $2,466.49 | $37,899.74 |
| Year 8 | $2,400.00 | $2,818.29 | $43,118.03 |
| Year 9 | $2,400.00 | $3,195.52 | $48,713.55 |
| Year 10 | $2,400.00 | $3,600.02 | $54,713.58 |
| Year 11 | $2,400.00 | $4,033.77 | $61,147.34 |
| Year 12 | $2,400.00 | $4,498.86 | $68,046.20 |
| Year 13 | $2,400.00 | $4,997.58 | $75,443.79 |
| Year 14 | $2,400.00 | $5,532.35 | $83,376.14 |
| Year 15 | $2,400.00 | $6,105.79 | $91,881.93 |
| Year 16 | $2,400.00 | $6,720.67 | $101,002.60 |
| Year 17 | $2,400.00 | $7,380.00 | $110,782.60 |
| Year 18 | $2,400.00 | $8,087.00 | $121,269.60 |
| Year 19 | $2,400.00 | $8,845.11 | $132,514.70 |
| Year 20 | $2,400.00 | $9,658.02 | $144,572.72 |
How it's calculated
Compound interest means you earn interest not just on your original principal, but also on the interest that's already been added. This calculator simulates growth period by period: each compounding period, interest is calculated on the current balance and added to it, and any contribution for that period is also added.
If you add contributions at the start of each period, they have slightly longer to earn interest within that period than contributions added at the end — which compounds into a meaningfully larger balance over many years.
Choosing a more frequent compounding schedule (like monthly instead of annually) slightly increases your final balance for the same stated annual rate, since interest is calculated and added more often.
Worked example
A $10,000 lump sum earning 5% annual interest, compounded monthly with no further contributions, grows to about $16,470 after 10 years.
Starting from that same $10,000 with a $200 monthly contribution at a 7% annual rate over 20 years, the balance grows to about $144,573 — $48,000 of that from your contributions and roughly $86,573 from compounding interest.
Frequently Asked Questions
- What's the difference between compound interest and simple interest?
- Simple interest is calculated only on your original principal. Compound interest is calculated on your principal plus any interest already earned, so your money grows faster over time.
- Does compounding frequency really matter?
- Yes, though usually by a modest amount. More frequent compounding (e.g. daily vs. annually) slightly increases your final balance for the same annual rate, because interest starts earning its own interest sooner.
- Should I contribute at the start or end of each period?
- Contributing at the start of each period gives that contribution slightly more time to earn interest within the period, which adds up to a larger balance over many years compared to contributing at the end.