Compound Interest Calculator (US)
See how your savings or investments grow with compound interest and regular monthly contributions, and what the final amount is worth in today’s money after inflation.
Updated for the 2026 tax year · Rates checked 14 October 2026
| Future balance | $300,851 |
|---|---|
| Total contributions | $130,000 |
| Total interest earned | $170,851 |
| Value in today's money | $183,600 |
- Interest makes up 57% of the final balance.
- With 2.5% yearly inflation, $300,851 in 20 years buys what $183,600 buys today.
Your result, explained
You would put in $130,000 and end up with $300,851. Growth earns $170,851 of that, 57% of the final balance. In today’s money it is worth about $183,600, because inflation slowly erodes purchasing power.
Time does most of the work in compounding: starting five years earlier often matters more than saving a little extra each month. Using a tax-free or tax-deferred account (a Roth IRA, ISA, TFSA, super or pension) keeps tax from interrupting the compounding.
Growth by year
| Year | Contributions | Interest | 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 |
| 11 | $6,000 | $7,905 | $120,544 |
| 12 | $6,000 | $8,910 | $135,455 |
| 13 | $6,000 | $9,988 | $151,443 |
| 14 | $6,000 | $11,144 | $168,587 |
| 15 | $6,000 | $12,383 | $186,971 |
| 16 | $6,000 | $13,712 | $206,683 |
| 17 | $6,000 | $15,137 | $227,820 |
| 18 | $6,000 | $16,665 | $250,486 |
| 19 | $6,000 | $18,304 | $274,790 |
| 20 | $6,000 | $20,061 | $300,851 |
Popular amounts
How compound interest works
Compound interest earns interest on your interest. Each period, interest is added to the balance, and the next period’s interest is calculated on that larger amount. Over long periods most of the final balance can come from growth rather than the money you put in.
The formula for a single deposit is A = P(1 + r/n)nt. With monthly contributions we simulate every month.
Tax-advantaged accounts
401(k), IRA and Roth IRA accounts grow tax-deferred or tax-free, which makes compounding work harder. This calculator shows growth before any tax.
Choosing a realistic rate
High-interest savings accounts pay roughly the central bank rate. A diversified stock portfolio has historically returned around 7% a year before inflation over long periods, but with big swings from year to year. Use a lower rate for a cautious plan.
Frequently asked questions
What is the rule of 72?
Divide 72 by your annual return to estimate how many years it takes to double your money. At 6% that is about 12 years.
Does compounding frequency matter?
A little. Daily or monthly compounding gives slightly more than annual compounding at the same stated rate. Contributions and time matter far more.
What does “today’s money” mean?
It is the future balance adjusted for inflation, showing what it would buy at today’s prices.