Compound interest calculator
Enter a starting sum and a monthly contribution to see what it compounds to — and what that is worth in today's money.
Works out how a starting sum and a regular monthly contribution grow at a given rate of return. A nominal figure always looks more generous than it is, so the value in today's money sits next to it. ₩1bn in thirty years is not ₩1bn now.
Your numbers
What you enter is saved in this browser, so it is still here next time
Used only to restate the total in today's money
Interest is added every month
After 20 years
What you end up with
₩264,122,492
Paid in and grown
- What you paid in
- ₩130,000,000
- What it grew by
- ₩134,122,492
- Times what you paid in
- 2.03×
In today's money
₩161,186,282
- Lost to inflation
- ₩102,936,210
Monthly contributions are treated as arriving at the end of the month. Paying at the start of the month earns one more month of interest, so the total comes out slightly higher.
Year by year
| Year | Paid in | Grown by | Balance | In today's money |
|---|---|---|---|---|
| Year 1 | ₩16M | ₩785K | ₩16.8M | ₩16.4M |
| Year 2 | ₩22M | ₩2M | ₩24M | ₩22.8M |
| Year 3 | ₩28M | ₩3.6M | ₩31.6M | ₩29.4M |
| Year 4 | ₩34M | ₩5.8M | ₩39.8M | ₩36M |
| Year 5 | ₩40M | ₩8.4M | ₩48.4M | ₩42.8M |
| Year 6 | ₩46M | ₩11.5M | ₩57.5M | ₩49.6M |
| Year 7 | ₩52M | ₩15.2M | ₩67.2M | ₩56.6M |
| Year 8 | ₩58M | ₩19.6M | ₩77.6M | ₩63.7M |
| Year 9 | ₩64M | ₩24.5M | ₩88.5M | ₩70.9M |
| Year 10 | ₩70M | ₩30.1M | ₩100.1M | ₩78.2M |
| Year 11 | ₩76M | ₩36.5M | ₩112.5M | ₩85.7M |
| Year 12 | ₩82M | ₩43.6M | ₩125.6M | ₩93.4M |
| Year 13 | ₩88M | ₩51.5M | ₩139.5M | ₩101.2M |
| Year 14 | ₩94M | ₩60.3M | ₩154.3M | ₩109.2M |
| Year 15 | ₩100M | ₩70M | ₩170M | ₩117.3M |
| Year 16 | ₩106M | ₩80.6M | ₩186.6M | ₩125.7M |
| Year 17 | ₩112M | ₩92.3M | ₩204.3M | ₩134.2M |
| Year 18 | ₩118M | ₩105M | ₩223M | ₩143M |
| Year 19 | ₩124M | ₩119M | ₩243M | ₩152M |
| Year 20 | ₩130M | ₩134.1M | ₩264.1M | ₩161.2M |
This assumes the same return every year. Real investments move up and down, and the same average return gives a different result depending on the order those moves come in. Tax and fees are not deducted.
Make a link with these numbers
Opening the link fills this screen with the same values. Useful for going through it with a partner, or for comparing two sets of conditions.
Common questions
QHow much difference does monthly compounding make?
At the same rate, the more often interest is added the more you end up with. 6% a year compounded monthly works out to an effective 6.17%. The gap widens over long periods, but it is smaller than the difference one percentage point of return makes.
QWhen is each contribution assumed to arrive?
At the end of the month. Paying at the start of the month earns one extra month of interest and ends up slightly higher. End-of-month is closer to how people actually save — whatever is left after payday — and it is the less optimistic of the two.
QIs tax included?
No. This is before Korea's 15.4% tax on interest and dividends, and before fees. Tax depends on the type of account, so look at the ISA·IRP calculator alongside this one.