Savings Plan Calculator with Bonus Contributions (Maturity Lump-Sum Tax)
Combine monthly contributions with extra bonus-month contributions and estimate your after-tax payout under a model that taxes all investment gains in a lump sum at maturity. See principal, interest, tax, and the monthly vs. bonus breakdown at a glance.
Last updated:
Input
yen
yen
times
years
%
%
Default is 20.315%, Japan's flat withholding tax.
Result
After-tax maturity payout (tax rate 20.315%)
14,447,841yen
Pre-tax maturity value is 15,275,849 yen
Total principal
11,200,000 yen
Investment gains (interest)
4,075,849 yen
Tax
828,009 yen
Breakdown by source (pre-tax maturity value)
Monthly portion
9,849,060 yen
Principal 7,200,000 yen
Bonus portion
5,426,789 yen
Principal 4,000,000 yen
How it works
- The maturity value of the monthly portion is found from the ordinary-annuity (end-of-period) formula FV = monthly contribution ร ((1 + r)^n โ 1) รท r, where the monthly rate r = annual rate รท 12 and the number of contributions n = savings years ร 12.
- The bonus portion is calculated the same way with FV = bonus contribution ร ((1 + rb)^nb โ 1) รท rb, where the per-period rate rb = annual rate รท bonuses per year and the number of contributions nb = savings years ร bonuses per year.
- The pre-tax maturity value is the FV of the monthly portion plus the bonus portion, the total principal is (monthly contribution ร n) + (bonus contribution ร nb), and investment gains (interest) = maturity value โ total principal.
- Tax applies only to investment gains, computed as interest ร tax rate (default is Japan's flat withholding tax of 20.315% = 15% income tax + 0.315% special reconstruction income tax + 5% resident tax) and deducted in a lump sum at maturity.
- The after-tax maturity payout is shown as the pre-tax maturity value minus the tax; when the annual rate is 0%, the total principal is treated as the maturity value itself.
- This is an estimate assuming monthly compounding and end-of-period contributions; it does not account for contribution timing, fees, various deductions, tax-law changes, or fluctuations in the actual rate of return, so the real payout may differ.
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