Savings & Deposit Interest Calculator — How to Calculate Maturity Interest (Simple & Compound, 15.4% Tax)
Jun 23, 2026
When a savings account or fixed deposit is about to mature, the question everyone wants answered is: "How much will I actually receive?" Many people are caught off guard when the amount that lands in their account is noticeably less than expected — after the 15.4% interest income tax is withheld. This guide explains how to calculate maturity interest for both regular savings accounts and fixed deposits, and how the 15.4% withholding tax is applied.
Enter your monthly deposit, interest rate, and term to see your maturity interest and after-tax payout instantly.
Savings & Deposit Calculator →Savings Account vs. Fixed Deposit — What's the Difference?
- Regular savings account (적금, jeokgeum) — You deposit a fixed amount each month. The first month's deposit earns interest for the full term, but the last month's deposit earns only one month of interest. Because the average holding period is roughly half the total term, the total interest earned is lower than a fixed deposit at the same rate.
- Fixed deposit (예금, yegeum) — You deposit a lump sum all at once. Interest accrues on the full principal for the entire term, making the calculation straightforward.
Simple Interest vs. Compound Interest
- Simple interest — Interest is calculated only on the principal. Intuitive to compute. Most regular savings accounts and fixed deposits in Korea use simple interest.
- Compound interest — Interest is also earned on previously accrued interest. The longer the term, the greater the advantage over simple interest. Some savings bank products and ISA accounts use compound interest.
How to Calculate — 2 Steps
- Choose your product type and interest method — In the Savings & Deposit Calculator, select either savings account or fixed deposit, and either simple or compound interest.
- Enter your amount, rate, and term — Input your monthly deposit (savings) or lump-sum principal (fixed deposit), the annual interest rate, and the term in months. Your maturity interest and after-tax payout appear instantly.
The 15.4% Interest Income Tax — Why Is It Withheld?
When interest is paid out, 15.4% is withheld at source as interest income tax. The breakdown is:
- Income tax 14% + Local income tax 1.4% = 15.4% total
The amount you actually receive — your after-tax interest — is the gross interest minus this 15.4%:
After-tax interest = Gross interest × (1 − 0.154)
Note: tax-exempt savings accounts (e.g., certain cooperative accounts) and ISA accounts may be treated differently, so verify the conditions before signing up.
Formulas — Illustrative Examples
The examples below use assumed values for illustration only. Actual returns depend on your specific product terms, preferential rates, and tax conditions.
| Type | Assumed values | Gross interest (simple) | After-tax interest |
|---|---|---|---|
| Savings acct. (simple) | ₩300,000/mo, 4% p.a., 12 months | approx. ₩78,000 300,000 × 0.04 × (12×13/2) / 12 |
approx. ₩66,012 |
| Fixed deposit (simple) | ₩5,000,000 lump sum, 4% p.a., 12 months | ₩200,000 5,000,000 × 0.04 × (12/12) |
₩169,200 |
※ The figures above are assumed values for illustrative purposes only. Actual payouts will vary based on your product terms, preferential rates, and tax conditions. No specific return is guaranteed.
Related Tools
If you're planning to use your matured savings to pay off a loan, check the Loan Interest Calculator to see your monthly repayment and total interest. For a detailed guide on loan interest calculations, see the Loan Interest Calculator blog post.
Savings or fixed deposit, simple or compound, 15.4% tax calculated automatically. Free.
Savings & Deposit Calculator →Frequently Asked Questions
Q. Do a savings account and a fixed deposit earn the same interest at the same rate?
No. Because a savings account receives monthly deposits, the average holding period is roughly half the total term. Using the simple interest formula — monthly deposit × annual rate × (months × (months + 1) / 2) / 12 — the total interest earned is lower than a fixed deposit at the same rate.
Q. Where and how is the 15.4% tax collected?
The bank withholds it automatically when paying out interest. Income tax (14%) and local income tax (1.4%) are combined into 15.4% and deducted in one go, so you receive the after-tax amount with no separate filing required.
Q. Is compound interest always better than simple interest?
Compound interest builds on itself and grows more advantageous the longer the term. For short-term products of one year or less, however, the difference between simple and compound interest is minimal — the interest rate itself and the tax conditions matter more.
Q. Is the data I enter sent anywhere?
No. All calculations run entirely in your browser — nothing is stored or transmitted to any server.