Compound Interest Calculator
Two modes — lump-sum and recurring (monthly deposits). A period-by-period and year-by-year schedule shows the profit, balance, and return at every step.
Compound Interest
Total profit
₩1,653,298
Final amount
₩2,653,298
Growth curve
| # | Profit (₩) | Balance (₩) | Return |
|---|---|---|---|
| 1 | +50,000 | 1,050,000 | 5.00% |
| 2 | +52,500 | 1,102,500 | 10.25% |
| 3 | +55,125 | 1,157,625 | 15.76% |
| 4 | +57,881 | 1,215,506 | 21.55% |
| 5 | +60,775 | 1,276,282 | 27.63% |
| 6 | +63,814 | 1,340,096 | 34.01% |
| 7 | +67,005 | 1,407,100 | 40.71% |
| 8 | +70,355 | 1,477,455 | 47.75% |
| 9 | +73,873 | 1,551,328 | 55.13% |
| 10 | +77,566 | 1,628,895 | 62.89% |
| 11 | +81,445 | 1,710,339 | 71.03% |
| 12 | +85,517 | 1,795,856 | 79.59% |
| 13 | +89,793 | 1,885,649 | 88.56% |
| 14 | +94,282 | 1,979,932 | 97.99% |
| 15 | +98,997 | 2,078,928 | 107.89% |
| 16 | +103,946 | 2,182,875 | 118.29% |
| 17 | +109,144 | 2,292,018 | 129.20% |
| 18 | +114,601 | 2,406,619 | 140.66% |
| 19 | +120,331 | 2,526,950 | 152.70% |
| 20 | +126,348 | 2,653,298 | 165.33% |
Final = initial × (1 + rate)^periods
Rate applies each time it compounds. Annual 5% monthly ≈ 0.42% × 120 periods (10y).
Pre-tax nominal. Income tax (15.4%) and inflation excluded.
What this tool does
The compound interest calculator covers two modes in one screen: lump-sum (a single principal compounding over time) and recurring (monthly deposits with compounding). The lump-sum mode uses FV = P(1+i)^n; the recurring mode offers annual compounding — matching the Korean bank savings-account convention where each month's deposit earns simple interest proportional to the remaining months, then all interest is capitalized at year-end — or monthly compounding. A period-by-period and year-by-year schedule shows the interest earned, running balance, and cumulative return at every step. Results are pre-tax nominal figures; withholding tax (15.4%) and inflation are not applied.
Who uses this
- Estimate the maturity value of a time deposit or savings account before signing up
- Project how much a monthly contribution to a pension savings plan or installment fund will grow over n years
- Back-calculate how long it will take (or how much to save per month) to reach a target amount
- Compare how much extra monthly vs. annual compounding earns for the same rate and period
- Visualize the compounding acceleration effect in the late years using the year-by-year schedule
How to use (3 steps)
- 1Select the tab: 'Lump-sum' or 'Recurring'. Lump-sum needs principal, rate per period, and number of periods. Recurring needs starting amount, monthly contribution, duration (years or months), rate (annual or monthly), and compounding frequency (annual or monthly).
- 2Click 'Calculate' to instantly see the final amount, total invested, total interest, and overall return rate in the summary cards.
- 3Switch between the 'Per-period' and 'Yearly' sub-tabs in the schedule below to trace interest, principal, and balance at every interval.
Formula & basis
[Lump-sum] FV = P × (1 + i)^n P = principal i = rate per period (% ÷ 100) n = number of periods With periodic contribution (PMT each period-end): FV = P×(1+i)^n + PMT × [(1+i)^n − 1] / i [Recurring — annual compounding (Korean savings-account convention)] Each monthly deposit earns simple interest of annual rate × (months remaining ÷ 12) within the year; the full balance is capitalized at year-end. [Recurring — monthly compounding] Balance is multiplied by (1 + monthly rate) every month, where monthly rate = annual rate ÷ 12.
Example scenarios
Example 1: ₩10,000,000 time deposit at 3.5% p.a. for 3 years
Lump-sum mode: principal ₩10,000,000, rate per period 3.5%, 3 periods (annual). Final amount = 10,000,000 × (1.035)^3 ≈ ₩10,877,289. Total interest ≈ ₩877,289 (8.77%). After Korean withholding tax of 15.4%, net interest is approximately ₩742,000.
Example 2: ₩500,000/month recurring, 4% p.a. annual compounding, 10 years
Recurring mode: starting ₩500,000, monthly ₩500,000, 10 years, 4% annual rate, annual compounding. Total invested ₩60,000,000; maturity ≈ ₩73,590,000; total interest ≈ ₩13,590,000 (22.6%). The yearly schedule shows that the 10th year alone generates ~₩2,700,000 in interest — the compounding acceleration effect in action.
Example 3: Annual vs. monthly compounding on the same principal
₩10,000,000 at 5% p.a. for 5 years: annual compounding → ₩12,762,816; monthly compounding → ₩12,833,587. Difference: ₩70,771. The gap widens with higher rates and longer durations, so it is worth checking the compounding frequency stated in a product's terms.
Frequently asked questions
Is monthly compounding always better than annual?
Yes, for the same stated annual rate. Monthly compounding capitalizes interest more frequently, so the effective annual rate (EAR) is higher. At 12% p.a., annual compounding gives EAR 12%, while monthly compounding gives EAR ≈ 12.68%. However, some products already advertise an effective monthly-compounded rate, so always read the product terms.
What is the 'Korean savings-account convention' for annual compounding?
Korean banks calculate interest on installment savings by crediting each monthly deposit with simple interest proportional to the number of months remaining in the year. The first month's deposit earns 12 months of interest; the last month's deposit earns 1 month. All accumulated interest is then capitalized at year-end (or maturity). The recurring annual-compounding mode in this calculator replicates that method.
Is withholding tax (15.4%) automatically deducted?
No. All results are pre-tax nominal amounts. In Korea, interest income is subject to 15.4% withholding (14% income tax + 1.4% local tax). To estimate after-tax interest, multiply the displayed total interest by 0.846.
How should I set 'rate per period' and 'periods' in lump-sum mode?
Match the period unit to the compounding frequency. For monthly compounding at 6% p.a. over 2 years: rate per period = 0.5% (6% ÷ 12), periods = 24. For annual compounding over 5 years at 5%: rate per period = 5%, periods = 5.
Is there a limit to the number of periods?
Lump-sum mode accepts up to 2,400 periods (200 years at monthly compounding). The per-period schedule table displays up to 600 rows; a notice appears when it is truncated. Recurring mode supports up to 1,200 months (100 years).
Why might the result differ from my bank's quoted figure?
This tool does not include withholding tax, transaction fees, inflation, or exchange-rate effects. For market products like funds or ETFs, returns are not fixed. Even for fixed-rate deposits, rounding rules (truncation vs. rounding at each step) can cause a difference of a few won versus the bank's own calculation.
Cautions
- •Pre-tax nominal calculation only — Korean withholding tax of 15.4% is not deducted. Estimate after-tax interest as total interest × 0.846.
- •Inflation is not factored in. Nominal return and real return differ.
- •In lump-sum mode, periodic contributions are assumed to be deposited at the end of each period. Products with beginning-of-period deposits will show slightly higher results.
- •The recurring annual-compounding model follows Korean bank savings-account convention. Minor differences may arise due to each institution's own rounding policy.
- •Results are for reference only. Confirm actual product terms with your financial institution or the FSS financial product comparison portal before subscribing.
Last reviewed: 2026-06-17