A folio of household instruments · Independent publication

Lake Oswego Finance Almanac Mortgage · Growth · Net Worth

Instrument the first

Mortgage Amortization Schedule

Set down a loan, a rate and a term, and see the payment, the full schedule, the curve of the balance and the interest that an extra monthly payment would save.

The terms of the loan

The amount borrowed after any down payment.

An illustrative value, not a quotation. Zero is allowed.

Whole years, from 1 to 50.

Paid on top of the regular payment, applied entirely to principal.

The starting values are illustrations for you to overwrite. They are not a lender’s offer and not a statement about current rates.

The result

Regular monthly payment principal and interest only

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Interest saved by the extra payment
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Time saved
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Payoff, as scheduled
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Payoff, with the extra
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Total interest, as scheduled
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Total interest, with the extra
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Total paid, with the extra
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Interest as a share of that total
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The balance, month by month

The solid line is the balance on the regular schedule. When an extra payment is entered, a dashed line shows the faster descent. Move the slider, or hover the chart, to read any month.

    The schedule, line by line

    Reading notes

    How to use this page, and what it assumes

    How to use it

    1. Enter the amount you expect to borrow, not the price of the property.
    2. Enter the yearly rate as a plain percentage, such as 5.25, and the term in whole years.
    3. Optionally add a fixed extra amount to be paid each month. Leave it at zero to see the loan as written.
    4. Read the payment and the totals, then scan the balance curve. The early flatness of the curve is the interest doing most of the work.
    5. Switch the table to monthly lines to see the exact split between principal and interest in any month.

    What it assumes

    • A fixed rate for the whole term, compounded monthly, with equal payments at the end of each month.
    • The extra payment is made every month from the first, and all of it reduces principal.
    • Property taxes, insurance, mortgage insurance, association dues, fees and closing costs are not included.
    • Figures are computed in floating point and displayed to the nearest cent. A lender’s rounding may differ by a few cents per payment.

    Edge cases

    • A rate of zero divides the loan evenly across all months, with no interest at all.
    • If the extra payment is larger than the remaining balance, the final payment is simply the balance plus its interest.
    • Adjustable rates, interest-only periods, balloon payments and recasts are not modelled; ask a lender how those terms would change the schedule.
    • Entries that are blank, negative, non-numeric or absurdly large produce a plain message rather than a result.

    This is arithmetic, not advice. The questions page explains the method in more detail.