Savings with tax every compounding

Apply tax at each compounding date and compare begin/end contribution timing with day-interval basis.

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Calculation basis and official references

Reviewed on:

Formula basis

Interest accumulates monthly as balance×annual rate/12. At each compounding month, tax=accrued interest×tax rate and capitalization=accrued interest−tax; 20.315% is the default for ordinary taxable deposit interest.

Calculation method

Accrues monthly interest on initial principal and contributions, deducts tax whenever the selected compounding date occurs, and capitalizes only after-tax interest.

Exclusions and checks required

  • Interest is monthly rather than actual-day; contribution ordering, per-compounding tax, and rounding are calculator assumptions.
  • The NTA source supports only the 20.315% default, not taxation at each compounding date or the calculation order.
  • Product accrual units, withholding rounding, tax exemptions, and changing rates are excluded.

Example input:：JPY 50,000 beginning-of-month contributions taxed each compounding date

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

Displayed tax uses monthly accrual and this implementation's per-compounding tax assumption.

Official references

FAQ

Who is this calculator for? Savings with tax every compounding

Apply tax at each compounding date and compare begin/end contribution timing with day-interval basis.

What values should I enter?

Applies to: Savings / Tax is withheld at every compounding date and only after-tax interest is capitalized.

How should I interpret this estimate?

Accrues monthly interest on initial principal and contributions, deducts tax whenever the selected compounding date occurs, and capitalizes only after-tax interest.

How to use

  1. Enter your input values and press Calculate.
  2. Review the result and compare it with expected context.
  3. Interest accumulates monthly as balance×annual rate/12. At each compounding month, tax=accrued interest×tax rate and capitalization=accrued interest−tax; 20.315% is the default for ordinary taxable deposit interest.

Official references