Saving & Investing
Compound Interest Calculator
See how a starting balance plus regular deposits grows over time, and how much of the final figure is contributions versus compounded growth.
Balance after 25 years
$381,283
$130,000 contributed · $251,283 growth
- Total contributed
- $130,000
- Total growth
- $251,283
- Growth share of balance
- 65.9%
- Deposits per year
- 12
$4,800 a year
Contributions vs growth
- Contributions — 34%
- Growth — 66%
| Year | Principal paid | Interest paid | Balance |
|---|---|---|---|
| 1 | $4,800 | $880 | $15,680 |
| 2 | $4,800 | $1,291 | $21,770 |
| 3 | $4,800 | $1,731 | $28,301 |
| 4 | $4,800 | $2,203 | $35,304 |
| 5 | $4,800 | $2,709 | $42,813 |
| 6 | $4,800 | $3,252 | $50,865 |
| 7 | $4,800 | $3,834 | $59,500 |
| 8 | $4,800 | $4,458 | $68,758 |
| 9 | $4,800 | $5,128 | $78,685 |
| 10 | $4,800 | $5,845 | $89,331 |
| 11 | $4,800 | $6,615 | $100,745 |
| 12 | $4,800 | $7,440 | $112,985 |
| 13 | $4,800 | $8,325 | $126,110 |
| 14 | $4,800 | $9,274 | $140,183 |
| 15 | $4,800 | $10,291 | $155,274 |
| 16 | $4,800 | $11,382 | $171,456 |
| 17 | $4,800 | $12,552 | $188,808 |
| 18 | $4,800 | $13,806 | $207,414 |
| 19 | $4,800 | $15,151 | $227,365 |
| 20 | $4,800 | $16,593 | $248,758 |
| 21 | $4,800 | $18,140 | $271,698 |
| 22 | $4,800 | $19,798 | $296,296 |
| 23 | $4,800 | $21,576 | $322,672 |
| 24 | $4,800 | $23,483 | $350,955 |
| 25 | $4,800 | $25,528 | $381,283 |
How the projection is built
The calculation steps through every period rather than using a single closed-form formula, so the deposit schedule and the growth line up exactly. In each period the balance is multiplied by (1 + r), where r is the annual rate divided by the number of periods per year, and then the deposit is added.
The growth figure is simply the final balance minus everything you put in. Over short horizons it is small; over 20 to 30 years it typically becomes the largest component of the balance, because each period's growth earns growth of its own.
Tax, platform fees and inflation are not modelled. Fees are best handled by lowering the rate — a 7% return with a 0.5% fee behaves like 6.5%.
Frequently asked questions
What does compounding frequency change?
Very little at ordinary rates. Monthly rather than annual compounding on 7% adds a fraction of a percent per year. Contribution size and time horizon dominate the outcome.
Are deposits added before or after growth?
Each period the balance grows first, then the deposit is added. This is the conservative convention and matches an end-of-period contribution.
Does this account for inflation or tax?
No. The result is in today's dollars at a nominal rate. To see purchasing power, enter a real rate — your expected return minus expected inflation.
Is the projected rate guaranteed?
No. It is an assumption you supply. Real returns vary year to year, so model a pessimistic scenario alongside your central one.