Handy tools
Interest Calculator
Recurring or lump-sum, simple or compound, with after-tax payout — enter a rate and term for instant maturity interest!
Work out what a monthly savings plan or a one-off deposit is worth at maturity. Pick simple or compound interest, enter the annual rate and term, and see total principal, interest before tax, tax withheld and the final payout.
Compound interest compounds monthly, and monthly deposits are counted from the start of each month. The tax presets are South Korean rates (15.4% = 14% income tax + 1.4% local tax; the 1.4% option for Korean cooperative deposits is the rural development tax only); your country may tax interest differently, so keep "No tax" to see the pre-tax figure. Works with any currency; bank fees and rounding are not included.
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The Giggleus savings interest calculator shows what a deposit is worth at maturity. Choose a monthly savings plan (the same amount paid in every month) or a lump-sum deposit, pick simple or compound interest, then enter the annual rate and the term in months (1–600). Total principal, interest before tax, tax and the final payout update as you type. Nothing is sent to a server.
Compound interest is compounded monthly. In a monthly savings plan each deposit only earns interest for the months it actually sits in the account: the first deposit earns for the full term, the last one for a single month. That is why 100 a month at 4% simple interest for 12 months earns 26, not 48. A 10,000 lump sum at 4% for 12 months earns 400 with simple interest and about 407 with monthly compounding.
The tax options follow South Korean rules: 15.4% standard, 1.4% for cooperative deposits, 9.5% tax-favored (closed to new accounts since 2015), or no tax. Outside Korea the default is "No tax", so the result is the pre-tax amount — apply your own country's rules separately. Amounts are plain numbers, so any currency works. Banks may round, charge fees or pay different rates for early withdrawal, so treat the result as an estimate.
Frequently Asked Questions
Q. What is the difference between simple and compound interest?
A. Simple interest is paid only on the money you deposited; compound interest is also paid on interest already earned. With 10,000 at 4% for 12 months, simple interest gives 400 and monthly compounding gives about 407 — the gap widens as the term gets longer.
Q. Why does a monthly savings plan earn less than the headline rate suggests?
A. Because each deposit earns interest only for the months it is in the account. Over 12 months the first deposit earns 12 months of interest and the last only 1, so 100 a month at 4% simple interest earns 26 in total, not 4% of 1,200.
Q. Which tax option should I choose?
A. The 15.4%, 1.4% and 9.5% presets are South Korean rates. If you are elsewhere, keep "No tax" (the default outside Korea) to see interest before tax and check your local rules separately.