Deposit & Savings Interest Calculator
Estimate maturity value by separating lump-sum deposits from monthly savings, simple from monthly compound interest, and gross from after-tax interest. Currency selection changes display units only and does not convert exchange rates.
Deposit and Savings Assumptions Versus Actual Bank Payout
Reference date and last reviewed: July 26, 2026
Calculation Basis
Applies the deposit principal or monthly contribution, annual rate, term, simple or monthly compound method, contribution timing, and selected interest-tax rate on a monthly basis. The Korean 15.4% preset combines 14% income-tax withholding with local income tax equal to 10% of that income tax.
Reference Limits
It does not determine exact day-count accrual, contribution dates, bank rounding, promotional-rate eligibility, early-withdrawal rates, tax-exemption eligibility, or aggregate-income taxation, so it cannot guarantee the actual payout or tax.
When to Confirm Officially
Before opening or closing an account or finalizing a maturity-fund plan, check the bank's product disclosure and maturity estimate for the interest method, promotional conditions, early-withdrawal rate, and tax treatment.
Usage Tips
Match the contribution date and tax treatment in the product terms
The same annual rate produces different maturity values for a lump-sum deposit and monthly savings, and for simple versus monthly compound interest. Check when each contribution starts earning and which tax rate applies, then compare gross interest with the estimated after-tax payout.
What is Deposit & Savings Interest Calculator?
The Deposit & Savings Interest Calculator estimates maturity value for a lump-sum deposit or recurring monthly contributions. Choose a display currency and enter the amount, annual rate, term, interest method, contribution timing, and tax rate to separate principal, gross interest, tax, net interest, and maturity value. Currency selection changes the unit and symbol without converting exchange rates.
How to Use
- 1Choose a lump-sum deposit or recurring monthly savings and select the product's display currency.
- 2Enter the deposit principal or the amount contributed each month.
- 3Enter the annual interest rate and term in months.
- 4Match the product terms by choosing simple or monthly compound interest and, for savings, beginning- or end-of-month contributions.
- 5Choose the Korean 15.4% preset, tax-free treatment, or a custom rate and review the gross and after-tax results.
Separate principal, gross interest, and after-tax maturity value
Last reviewed: July 26, 2026Simple-interest formulas for deposits and monthly savings
deposit interest = principal × annual rate ÷ 12 × n; beginning savings interest = monthly contribution × annual rate ÷ 12 × n(n+1) ÷ 2
A deposit earns on the full principal for the same term. Recurring contributions earn only for their remaining months, so the calculator sums those different interest periods.
A 10,000 deposit at 3.5% for 12 months
- • Deposit principal 10,000
- • 3.5% annual rate and 12-month simple interest
- • Selected tax rate 15.4%
- 1. Gross interest = 10,000 × 0.035 ÷ 12 × 12 = 350
- 2. Estimated tax = 350 × 0.154 = 53.90
- 3. Net interest = 350 - 53.90 = 296.10
The estimated after-tax maturity value is 10,296.10: principal of 10,000 plus net interest of 296.10.
How to read the result
- The maturity value is not all profit; compare total principal with net interest separately.
- For recurring savings, later contributions earn for fewer months even at the same annual rate.
Conditions that change the result
- This monthly model does not reproduce exact calendar-day accrual or every bank's rounding convention.
- It does not determine promotional-rate eligibility, early-withdrawal rates, tax-exemption eligibility, or aggregate-income taxation.
Common input mistakes
- Enter 3.5 for a 3.5% user-facing rate, not the decimal 0.035.
- Do not enter total planned savings as the monthly contribution; doing so multiplies it by the number of months.
Reference Knowledge
- ●Deposit simple interest = principal × annual rate ÷ 12 × number of months
- ●Beginning-of-month savings simple interest = monthly contribution × annual rate ÷ 12 × n(n+1) ÷ 2
- ●Net interest = gross interest - gross interest × entered tax rate
- ●The Korean 15.4% reference preset combines 14% income-tax withholding and local income tax equal to 10% of that income tax.
FAQ
Q.Why do a deposit and monthly savings earn different interest at the same rate?
The full deposit principal earns for the entire term. Each recurring contribution earns for a different, shorter period, so recurring savings generally produces less gross interest even when total contributions and the annual rate are the same.
Q.Should I choose beginning- or end-of-month contributions?
Choose beginning of month when the first payment is made at opening and each contribution is assumed to earn for that month. Choose end of month when a payment begins earning in the next month. A bank may instead use the exact payment date and a daily accrual convention.
Q.Does the 15.4% preset apply to every savings product?
No. It is a reference for ordinary Korean deposit-interest withholding. Tax-exempt accounts, policy products, cooperative deposits, and products in other jurisdictions can use different rates and eligibility rules.
Q.Why can the bank's maturity estimate differ?
A bank may use exact day counts, individual contribution dates, promotional-rate eligibility, rounding rules, and early-withdrawal rates. This calculator applies the entered assumptions consistently by month for comparison.
