Korean Installment Savings Early/Late Payment Calculator
Calculate your real maturity date and interest from early and late installment payments
This calculator models Korea's seonnap-iyeon strategy for installment savings accounts: pay some installments early and others late, and it tallies the resulting early-days and late-days totals to show whether your maturity date slips and exactly how much interest you'll earn before and after tax. Pick a well-known pattern like the 6-1-5 rule or the 1-11 rule, or edit each installment's actual payment date to build your own simulation — ideal for savers who park idle cash in a CMA account and want to squeeze maximum efficiency out of their savings interest. Everything is calculated in your browser, and the amounts and dates you enter never reach a server.
🔒 Everything runs 100% in your browser. Your files and input are never uploaded to any server.
How to use
- Enter your monthly deposit, the contracted annual interest rate, and the account opening date.
- Pick a payment pattern: the 6-1-5 rule, the 1-11 rule, or standard on-time payments.
- If you'd like, edit the actual payment dates directly in the installment table to build your own simulation.
- Review your total early days and late days, your real maturity date, and pre-tax and after-tax interest, then copy the results.
FAQ
- What is the 6-1-5 rule?
- It's the best-known early/late payment strategy: you front-load six months' worth of deposits on the first installment, pay the remaining five months' worth on the seventh installment, and top up the balance on the final installment — maximizing your accumulated early days.
- What happens if my early days exceed my late days?
- As long as total early days are greater than or equal to total late days, your maturity date doesn't slip and you can close the account at maturity at the full contracted rate. This calculator shows that net difference right away.
- Can I change the payment date for individual installments?
- Yes. Edit any installment's actual payment date in the table and the pattern automatically switches to 'Custom,' with the results recalculated to match.