Compound Interest & Savings Calculator
Project your maturity value before and after tax from an initial lump sum, monthly contributions, interest rate, term, and compounding frequency.
Whether you're parking a lump sum, adding a fixed amount every month, or doing both, this calculator shows what your money grows into by maturity. Choose your compounding frequency (monthly, quarterly, or annual) and your tax treatment — Korea's standard 15.4% interest income tax, the 9.5% preferential rate, or a tax-free account such as an ISA — and get an instant after-tax total plus a year-by-year growth table.
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How to use
- Enter your initial lump sum and the amount you plan to contribute each month.
- Set the annual interest rate (%) and how many years you'll stay invested.
- Pick a compounding frequency (monthly, annual, and so on) and a tax option (standard, preferential, or tax-free) to see your projected after-tax balance at maturity.
FAQ
- What's the difference between simple and compound interest?
- Simple interest is earned on your original principal only. With compound interest, the interest earned each period is added back to the principal and starts earning interest itself. The longer your money stays invested, the more dramatically compounding accelerates growth.
- How much does tax treatment actually change the outcome?
- Under Korea's standard treatment, 15.4% of your interest is withheld as tax. In a tax-free or ISA account, the interest income tax rate is 0%, so you keep every won of interest you earn — a gap that widens substantially over long terms.
- With the same interest rate and term, how much does the compounding frequency (monthly vs. yearly) actually change the final amount?
- The more often interest gets folded back into the principal — monthly beats quarterly, which beats yearly — the more often it starts earning interest of its own, so the final payout ends up slightly higher. That gap is barely noticeable at low rates over short terms, but it widens meaningfully at higher rates over longer periods.