Compound Interest Calculator
Estimate how your savings, investment account, 401(k), or retirement fund could grow over time.
After 20 years, your estimated balance could be
$56,435.28
You contributed $25,000.00 yourself. The remaining $31,435.28 comes from estimated compound growth. This shows how regular contributions and time can work together to build long-term value.
Balance over time
Year-by-year breakdown
| Year | Contributions | Growth | Balance |
|---|---|---|---|
| 1 | $2,200.00 | $118.78 | $2,318.78 |
| 2 | $3,400.00 | $332.89 | $3,732.89 |
| 3 | $4,600.00 | $649.23 | $5,249.23 |
| 4 | $5,800.00 | $1,075.18 | $6,875.18 |
| 5 | $7,000.00 | $1,618.68 | $8,618.68 |
Formula
Compound interest is calculated as A = P(1 + r/n)nt,
where P is the initial amount, r is the annual rate as a decimal,
n is the number of compounding periods per year, and t is the number of years.
With regular monthly contributions, the calculation runs iteratively period-by-period to add each contribution and apply interest.
Worked example
Starting with $1,000.00, adding $100.00 per month at 7% annual return for 20 years with monthly compounding produces an estimated final balance of $56,435.28 ($25,000.00 contributed plus $31,435.28 in compound growth).
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Frequently asked questions
What is compound interest?▾
Compound interest is interest earned on both your initial deposit and on interest already added to the balance. Over long periods, it can grow your savings far faster than simple interest.
Does this calculator account for US tax (401(k), IRA, capital gains)?▾
No. Results are pre-tax estimates. 401(k) and traditional IRA contributions are typically pre-tax (taxed on withdrawal); Roth accounts are post-tax. Brokerage account gains may be subject to capital gains tax. Consult a tax professional for specifics.
Can I include monthly contributions?▾
Yes. Enter your regular monthly contribution and the calculator iteratively adds it to your balance each month before applying interest.
Are investment returns guaranteed?▾
No. Investment returns are not guaranteed and may go down as well as up. The rates you choose are assumptions only — historical S&P 500 returns have averaged ~7% real, but past performance does not predict future results.