Compound Interest Calculator
Last updated: 2026-06-25
When you contribute a fixed amount each month and let it compound, the future value is the sum of each contribution grown over its remaining time. With monthly return r and n months, contribution future value = monthly contribution × [((1+r)^n − 1) ÷ r] × (1+r).
Add initial investment × (1+r)^n for the total future value. The longer the period, the larger the compounding effect.
Enter contribution details
Estimated future value (pre-tax)
0 KRW
| Item | Amount |
|---|---|
| Total contributed principal | |
| Initial investment | |
| Total gains (compounding) | |
| Total future value |
The return is an assumption that is not guaranteed. This is a pre-tax, nominal figure that does not reflect taxes or inflation. Results are a reference simulation.
How to use
- Enter contribution details — enter your monthly contribution, expected annual return (%) and investment period (years).
- Enter initial investment — if you have a lump sum to invest up front, enter it (otherwise 0).
- View results — press "Calculate future value" to see the future value, total contributed principal and total gains in a table.
How regular investing with compounding works
Regular investing means contributing a fixed amount consistently each month. Money contributed earlier compounds for longer, so for the same total principal, starting earlier yields a larger future value. This is why people say "time is return."
| Period | Total principal | Future value |
|---|---|---|
| 10 years | 60M KRW | ~86.8M KRW |
| 20 years | 120M KRW | ~260.9M KRW |
| 30 years | 180M KRW | ~610M KRW |
As the table shows, principal grows in proportion to the period, but the future value grows much faster thanks to compounding. Note that this assumes a constant annual return while real markets fluctuate. If you want to know how long a return takes to double your money, use the Rule of 72 Calculator; for ROI and tax basics, see the investing guide.
Frequently asked questions (FAQ)
How is the future value of regular investing calculated?
When you contribute a fixed amount each month, the future value is the sum of each contribution compounded over its remaining time. With monthly return r (= annual return ÷ 12) and n months, contribution future value = monthly contribution × [((1+r)^n − 1) ÷ r] × (1+r) (begin-of-period contributions), plus initial investment × (1+r)^n.
What is the difference between compound and simple interest?
Simple interest accrues only on the principal, while compound interest earns interest on interest. The longer the period, the larger the compounding effect and the wider the future-value gap. Regular investing adds new principal each month with compounding on top, so it gets more favorable over the long run.
Does this calculator account for taxes and inflation?
This calculator shows a pre-tax, nominal future value. In reality you should also consider dividend tax (15.4%), overseas-stock capital gains tax, and the loss of real value from inflation. The result is a reference simulation based on an assumed return.
How should I choose a return rate?
The return is an assumption not guaranteed in the future. Reference long-term historical stock market averages (roughly 5%–8% per year), but it is safer to simulate conservatively with a lower figure. It is recommended to run multiple return scenarios to see a range.
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Last updated: 2026-06-25