Addon repayment

Calculate monthly payment, total payment, total interest, and equivalent annualized nominal rate from addon rate.

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Calculation specification

Reviewed on:

Formula basis

Interest=P×a×m/12, total=P+interest, and the unrounded monthlyPaymentExact=total/m. For the effective annual rate conversion, a periodic rate i satisfying P=monthlyPaymentExact×{1−(1+i)^−m}/i is solved numerically and displayed as 12i.

Calculation method

Adds addon interest for the full term to principal, divides the total into equal monthly payments, and derives an equivalent declining-balance nominal annual rate.

Exclusions and checks required

  • An addon annual rate is not a declining-balance effective rate; the effective annual rate conversion assumes monthly annuity payments and uses unrounded monthlyPaymentExact, not the displayed rounded monthly amount.
  • Fees, irregular first or final payments, prepayment, and actual-day accrual are excluded.

Example input:：JPY 1 million at a 6% addon rate for 36 months

annualAddonRate
6
months
36
principalMan
100
rounding
halfUp

The converted rate uses unrounded monthlyPaymentExact and is unaffected by display rounding, while the displayed monthly and total amounts may differ because of yen rounding.

FAQ

Who is this calculator for? Addon repayment

Calculate monthly payment, total payment, total interest, and equivalent annualized nominal rate from addon rate.

What values should I enter?

Applies to: Addon loans / Interest = principal × addon annual rate × number of months / 12

How should I interpret this estimate?

Adds addon interest for the full term to principal, divides the total into equal monthly payments, and derives an equivalent declining-balance nominal annual rate.

How to use

  1. Enter your input values and press Calculate.
  2. Review the result and compare it with expected context.
  3. Interest=P×a×m/12, total=P+interest, and the unrounded monthlyPaymentExact=total/m. For the effective annual rate conversion, a periodic rate i satisfying P=monthlyPaymentExact×{1−(1+i)^−m}/i is solved numerically and displayed as 12i.