Compound Interest & Savings
Projects the value of a lump sum or regular deposits at a given rate, with a year-by-year table.
Projects what a lump sum or a regular deposit turns into at a given rate, year by year, with Korean 이자소득세 taken off if you want it. It covers the three Korean products separately — 정기예금, 정기적금 and true compounding — because they are not the same calculation and mixing them up is why the bank’s figure never matches.
What are you working out
Numbers
Projection
you put in
70,000,000
interest earned
7,375,541
tax withheld
1,135,833
final value
76,239,708
effective annual rate
3.557%
doubling time
20.1 years
rule of 72 says 20.6
Year by year
| Year | Opening | Deposits | Interest | Closing |
|---|---|---|---|---|
| 1 | 10,000,000 | 12,000,000 | 550,053 | 22,550,053 |
| 2 | 22,550,053 | 12,000,000 | 996,421 | 35,546,474 |
| 3 | 35,546,474 | 12,000,000 | 1,458,664 | 49,005,138 |
| 4 | 49,005,138 | 12,000,000 | 1,937,347 | 62,942,485 |
| 5 | 62,942,485 | 12,000,000 | 2,433,056 | 77,375,541 |
How to use it
Pick the product
Compound interest, 정기적금 or 정기예금. The Korean products use simple interest by convention, which is why a 3% 적금 does not pay 3% of your total deposits.
Put in the numbers
Starting amount, monthly deposit, annual rate and term. The rate is always the annual one; the compounding frequency is separate. Every box takes one number, read the way this page’s language writes one: the rate goes in as 3.5 here, and as 3,5 on the pages that mark the decimal with a comma. An amount pasted with its thousands separators — 10,000,000 — goes in as it is.
Decide about tax
Korean interest income is taxed at 14% plus a 1.4% local surtax, taken at maturity. With it on you see what actually lands in the account.
Read the year-by-year table
It separates what you put in from what the interest added, which is the only honest way to see whether a rate is doing any work.
Common questions
Why is my 적금 interest so much less than I expected?
Because each deposit only earns for the months it is actually in the account. The last month’s deposit earns one month of interest, not twelve. A 3% twelve-month 적금 pays roughly 1.6% of your total deposits before tax.
What does compounded monthly actually change?
It adds the interest to the balance twelve times a year instead of once, so the next month earns on a slightly larger number. At 5% that turns an annual 5% into an effective 5.12%. The tool shows the effective annual rate for whatever you pick.
Is inflation taken into account?
No. Everything here is nominal. At 3% interest and 3% inflation the balance grows and the purchasing power does not, and that is a separate calculation this tool does not attempt.
Does the rule of 72 work?
Well enough between about 4% and 12%. The tool shows both the rule’s answer and the exact doubling time, so you can see where the approximation drifts.
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