Bonus-savings with tax each compounding

Combine monthly and bonus savings, then tax interest at each compounding period.

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Calculation basis and official references

Reviewed on:

Formula basis

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

Calculation method

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

Exclusions and checks required

  • Fixed semiannual bonuses, annual rate/12 interest, tax at compounding, and rounding are implementation assumptions.
  • The NTA source supports only the 20.315% default, not bonus timing or per-compounding taxation.
  • Product-specific accrual, withholding rounding, exemptions, and fees are excluded.

Example input:：Beginning-of-month regular and bonus savings taxed each compounding date

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

Balance and tax depend on this calculator's monthly event order and rounding.

Official references

FAQ

Who is this calculator for? Bonus-savings with tax each compounding

Combine monthly and bonus savings, then tax interest at each compounding period.

What values should I enter?

Applies to: Savings / Bonus top-ups and period-tax compounding are both simulated month-by-month.

How should I interpret this estimate?

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

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, tax at each compounding date, and yen rounding are applied separately to each balance before the results are summed. Each balance's tax is accrued interest×tax rate, with 20.315% as the default.

Official references