Project how your savings or investments grow with lump sums and regular contributions. Runs locally.
Grey = money you put in · Teal = compound growth.
How to use the compound interest calculator
Enter your starting balance, the amount you add each period, the annual rate, and the number of years. The calculator shows the final balance and how much of it came from your contributions versus the interest earned on top.
Why compounding snowballs
Interest earns interest. In the early years the growth looks modest, but as the balance grows, each period’s interest is calculated on a bigger number. Time matters more than the rate — an extra five years often beats chasing an extra percentage point.
Tips to make it work for you
Start as early as you can, even with small amounts, and keep contributions consistent. Reinvesting dividends or interest rather than withdrawing keeps the snowball rolling, and avoiding high fees preserves more of the compounding effect.
How compound interest works
Compound interest means you earn returns not just on your original money but on the returns it has already earned. The core formula for a lump sum is:
A = P × (1 + r/n)^(n×t)
where P is the principal, r is the annual rate, n is how often interest compounds per year and t is the years. The calculator also supports regular contributions — deposits added on a schedule — which is how most people actually save. It then splits the final balance into the money you put in versus the interest it generated, so you can see compounding do the heavy lifting.
Common uses
- Retirement savings — project how monthly contributions grow over decades.
- Emergency funds — see what a high-yield account could return.
- Education funds — estimate a future balance for a child’s college.
- Debt comparison — understand how compounding works against you on balances you carry.
Frequently asked questions
What does “compounding frequency” mean?
It is how often interest is added to your balance. Daily compounding grows slightly faster than annual, all else equal.
Is this the same as APY?
APY is the effective annual rate once compounding is included. This calculator shows both the math and the resulting growth.
Do contributions have to be monthly?
No. You can model any regular schedule; more frequent contributions start compounding sooner.
Are taxes or inflation included?
No. This shows nominal growth. Real purchasing power is lower after taxes and inflation, which is worth keeping in mind for long horizons.
What return rate should I assume?
Use a realistic long-run figure: often 6–8% for diversified stock investments before inflation, and the stated rate for savings accounts or bonds. Planning with conservative numbers beats optimistic ones you can’t actually achieve.
How much difference does compounding frequency really make?
Over long periods and higher rates the gap between annual and daily compounding can be noticeable, because interest starts earning its own interest sooner rather than once a year.
How compounding frequency changes the result
| Frequency | Periods per year | Effect on growth |
|---|---|---|
| Annually | 1 | The baseline figure |
| Semi-annually | 2 | Slightly more than annual |
| Quarterly | 4 | More again |
| Monthly | 12 | The usual figure for savings |
| Daily | 365 | Marginal gain over monthly |
| Continuously | Infinite | The mathematical ceiling |