How this calculator works
Every row starts with the opening balance, adds periodic interest, then applies the scheduled payment and any eligible extras. The last payment is reduced to clear only what remains due. Annual rows group full payment years from the first due date, rather than calendar years. Unlike a simple loan summary, this schedule supports Canadian compounding, accelerated frequencies, dated lump sums and carrying-cost budgeting. The interface displays the first 500 periodic rows; annual rows cover the full plan.
Formula
Interest in period k = opening balance × periodic rate. Principal repaid = actual payment - interest. Closing balance = opening balance - principal repaid. Periodic rate = (1 + r/c)^(c/f) - 1. Total interest is the sum of the interest column; total principal is the opening mortgage.
Worked example
An $80,000 mortgage at 0% over 120 monthly payments has $666.67 principal in each full payment and no interest. A $200 lump sum on the first payment of a $1,200, twelve-month 0% loan leaves ten payments in total.
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Frequently asked questions
Why does the interest portion fall?
With a positive fixed rate, a smaller balance produces less interest. A level payment then sends more money to principal.
Are annual rows calendar years?
No. They group the first twelve monthly payments, first 26 biweekly payments or corresponding payment-year count.
Why does this differ from my statement?
The estimate keeps full precision and equal periodic interest. Lender cent rounding, daily accrual, holidays and future renewals can change statement balances.