Bonus-savings with maturity lump-sum tax

Add bonus contributions every six months on top of monthly savings and tax all interest at maturity.

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Calculation basis and official references

Reviewed on:

Formula basis

The monthly and bonus balances are compounded independently; monthly interest, maturity tax, and yen rounding are applied separately to each balance before the results are summed. Each balance's maturity tax is cumulative interest×tax rate, with 20.315% as the default.

Calculation method

Computes monthly contributions (including initial principal) and fixed semiannual bonus contributions as independent balances, then sums their maturity balances.

Exclusions and checks required

  • Bonus contributions are fixed every six months from the selected starting month.
  • The NTA source supports only the 20.315% default, not maturity taxation, compounding intervals, or rounding.
  • Actual bonuses, product accrual and tax rules, fees, and changing rates are excluded.

Example input:：JPY 50,000 monthly plus JPY 200,000 semiannually

annualRate
1.2
rounding
floor
years
10
monthlyMan
5
bonusMan
20
bonusStartMonth
6
initialPrincipalMan
100
compounding
monthly
taxMode
maturity
taxRate
20.315

The maturity value assumes fixed bonuses and one tax deduction at maturity.

Official references

FAQ

Who is this calculator for? Bonus-savings with maturity lump-sum tax

Add bonus contributions every six months on top of monthly savings and tax all interest at maturity.

What values should I enter?

Applies to: Savings / Bonus top-ups are added every six months from the selected start month.

How should I interpret this estimate?

Computes monthly contributions (including initial principal) and fixed semiannual bonus contributions as independent balances, then sums their maturity balances.

How to use

  1. Enter your input values and press Calculate.
  2. Review the result and compare it with expected context.
  3. The monthly and bonus balances are compounded independently; monthly interest, maturity tax, and yen rounding are applied separately to each balance before the results are summed. Each balance's maturity tax is cumulative interest×tax rate, with 20.315% as the default.

Official references