Compound Interest Calculator
See what regular contributions plus compound growth turn into over time — and how much of the total is growth rather than deposits.
Your details
Details
Bump your monthly deposit each year to keep pace with raises
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
Balance after 25 years
$462,290
$302,290 of that is growth — 65.4% of the final balance
Includes your inputs, the full breakdown, and every row of the table.
Total contributed
$160,000
Total growth
$302,290
Growth multiple
2.89×
Final balance ÷ money you put in
Effective monthly rate
0.583%
- Starting amount
- $10,000
- Deposits over time
- $150,000
- Total you contributed
- $160,000
- Compound growth
- $302,290
- Final balance
- $462,290
| Year | Contributed | Growth | Balance |
|---|---|---|---|
| 1 | $6,000 | $919 | $16,919 |
| 2 | $6,000 | $1,419 | $24,339 |
| 3 | $6,000 | $1,956 | $32,294 |
| 4 | $6,000 | $2,531 | $40,825 |
| 5 | $6,000 | $3,148 | $49,973 |
| 6 | $6,000 | $3,809 | $59,782 |
| 7 | $6,000 | $4,518 | $70,299 |
| 8 | $6,000 | $5,278 | $81,578 |
| 9 | $6,000 | $6,094 | $93,671 |
| 10 | $6,000 | $6,968 | $106,639 |
What this means
- Contributions are treated as deposits at the end of each month, which is the conservative assumption.
- Returns are shown before taxes, fees, and inflation. A steady annual return is a modelling convenience — real markets do not move in a straight line.
How the compound interest calculation works
Compound interest is the reason time in the market matters more than timing it. Each period's growth is calculated on the balance you already have, including all previous growth — so the curve bends upward rather than climbing in a straight line.
The most useful number on this page is often not the final balance but the split between what you contributed and what the growth added. Early on, your deposits dominate. Somewhere in the middle the growth line crosses your contribution line, and from that point onward your balance is mostly money you never earned at a job.
The yearly contribution increase is worth experimenting with. Raising your monthly deposit by even 3% a year — roughly a typical cost-of-living raise — usually beats chasing an extra percentage point of return, and it is entirely within your control.
Frequently asked questions
What return rate should I use?
For a diversified stock portfolio, 6–7% after inflation or 9–10% before it are common long-run planning figures. For bonds or cash, use something far lower. If the result only works at 12%, the plan is fragile.
Does compounding frequency matter much?
Less than most people expect. At 7%, moving from annual to daily compounding changes the effective annual rate by roughly a quarter of a percentage point. Your contribution rate matters far more.
Is this before or after taxes?
Before. In a 401(k) or IRA the growth is sheltered until withdrawal. In a taxable brokerage account, dividends and realised gains are taxed along the way, which drags the real curve below this one.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.