Interest Rate: 8.5%
The effective annual rate,
e = (1 + 0.085/2)^2 - 1
and the monthly rate is,
r = (1 + e)^(1/12) - 1 = 0.00696106
Payment Frequency: Monthly
y = 10
The calculation can be made:
Payments for months 1 to 6 of each year are $1,934.20
Payments for months 7 to 12 of each year are $500
Note the calculation above does not reduce to a convenient formula as does the case with equal repayments, i.e.
Dividing top and bottom by
(1 + r)^n produces the Loan Payment Formula:
Calculation with an interest holiday in the low season
It's not straightforward applying this to the method used by the Hema calculation in the Seasonal Loan Amortization post because the Hema calculator gives an interest holiday in the low season. (That is how their calculation works out to 24 periods over 3 years. For 12 periods there are no payments and neither is any interest charged on the balance, through Sept to Dec).
If fixed payments are to be made in the low season in the present case, with no interest charges on the balance in months 7 to 12, the payments in months 1 to 6 can be worked out like this: