Compound Interest Calculator
Also works as a savings calculator: enter an initial deposit and a monthly contribution to see your balance grow year by year — and how much of it is interest doing the work.
Ending balance
$107,144
After 10 years at 7% APY, compounding monthly.
Year by year
| Year | Contributed | Interest | Balance |
|---|---|---|---|
| 1 | $6,000 | $955 | $16,955 |
| 2 | $6,000 | $1,458 | $24,413 |
| 3 | $6,000 | $1,997 | $32,411 |
| 4 | $6,000 | $2,575 | $40,986 |
| 5 | $6,000 | $3,195 | $50,182 |
| 6 | $6,000 | $3,860 | $60,042 |
| 7 | $6,000 | $4,573 | $70,614 |
| 8 | $6,000 | $5,337 | $81,952 |
| 9 | $6,000 | $6,157 | $94,108 |
| 10 | $6,000 | $7,036 | $107,144 |
Common questions
What is the difference between APY and APR?
APY (annual percentage yield) includes the effect of compounding — it's what your money actually grows by in a year. APR (annual percentage rate) doesn't include compounding, so a 7% APY savings account earns more than a 7% APR loan costs over the same period. Enter the APY your bank quotes.
What is the rule of 72?
A quick mental shortcut: divide 72 by your annual rate to estimate how many years it takes money to double. At 7%, that's about 10.3 years. It works because ln(2) ≈ 0.693 — 72 is just a nearby number with lots of divisors.
Is it better to start early or contribute more later?
Starting early almost always wins, because compounding is exponential — early contributions get the most doubling cycles. Try it above: $200 a month from age 25 to 35 beats $200 a month from 35 to 65 at the same rate, even though the late starter contributes three times as much.