💰 Compound Interest Calculator
Compare gross and after-tax savings growth or estimate the principal needed for a target income.
Calculation settings
Contributions are assumed to be made at the beginning of each month.
Each period's interest is assumed to be added to principal for the next period.
This share of each day's gross interest is added to the next day's principal.
No tax adjustment is applied by default. Enter the rate that fits your situation.
Results
Provider rounding, promotional terms, and actual crediting dates can change the final amount.
Deposited principal plus estimated after-tax interest.
- Deposited principal
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- Gross interest
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- Estimated tax
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- After-tax interest
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- Gross effective annual rate
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- After-tax effective annual rate
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Estimated principal for — of monthly average after-tax interest.
- Required principal
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- Daily after-tax interest
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- 28–31 day after-tax range
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- Annual after-tax interest
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- After-tax effective annual rate
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If an individual's annual taxable interest and dividend income exceeds KRW 20 million in total, it may be combined with other comprehensive income.
| Tax base | Rate |
|---|---|
| Up to KRW 14 million | 6% |
| Over 14m–50m | 15% |
| Over 50m–88m | 24% |
| Over 88m–150m | 35% |
| Over 150m–300m | 38% |
| Over 300m–500m | 40% |
| Over 500m–1bn | 42% |
| Over KRW 1 billion | 45% |
These are national base rates; local income tax is separate. Actual treatment depends on all financial income, other comprehensive income, deductions, and exceptions. This notice does not change the tax-rate input automatically.
Calculation assumptions
Use these assumptions when comparing the estimate with a financial product.
- Interest methodSimple interest uses the original principal, compound interest reinvests at the selected frequency, and the custom reinvestment rate adds only part of each day's gross interest to the next day's principal.
- Recurring contributionsThe same amount is assumed to be deposited at the beginning of each month.
- Tax and roundingThe custom tax rate is applied to total interest; provider-specific rounding and account rules are not included.
Frequently Asked Questions
▼Compound interest adds all interest to principal at the selected daily, monthly, or yearly frequency. The custom reinvestment method adds only the entered share of each day's gross interest to the following day's principal. Entering 100% switches the calculator to daily compounding.
The monthly-average option uses 365 days divided by 12. The result also shows a 28-to-31-day after-tax range so you can see how calendar month length changes the estimate.
A lump sum earns interest on the full starting balance for the whole term. Recurring contributions are added at the beginning of each month, so every deposit has a different time to earn interest.
Tax treatment depends on country, account type, and personal circumstances. The English page makes no tax-jurisdiction assumption, so enter the rate that applies to your estimate. If KRW is selected and annualized gross interest on the current principal exceeds KRW 20 million, an information icon shows a Korean comprehensive-income-tax reference; it is not an automatic tax calculation.
Use it to compare simple and compound growth, estimate gross and after-tax interest, or work backward from a desired daily, monthly, or annual interest amount. Confirm final terms with the account provider.