By the CalcLedger editorial team · Updated September 2026 · Examples use illustrative rates · How we calculate
Open any 30-year mortgage's amortization schedule and the first line often surprises new homeowners: on a $320,000 loan at 6.9%, roughly $1,840 of the first payment goes to interest, and only about $280 actually reduces the balance. That ratio doesn't stay fixed — it shifts every single month, and understanding why explains a lot about how mortgages, and debt in general, behave.
Interest is charged on what's left, not what you started with
Every month, your lender calculates interest on your current balance — not your original loan amount. Early on, when your balance is close to the full loan amount, the interest portion is large. As the balance shrinks, the interest charge shrinks with it, and more of each fixed payment is freed up to attack the principal. This is why the split between principal and interest moves gradually over the life of the loan, even though your total payment stays flat.
Why this matters if you might move or refinance
Because so little of the early payments builds equity, selling or refinancing in year 2 or 3 of a 30-year mortgage means you've paid down surprisingly little principal — most of what you paid went to the lender as interest, not into your home. This is one reason a shorter loan term or a larger down payment matters more than it might seem: both reduce the amount of interest-heavy early payments you're making.
What actually speeds up the curve
Extra payments applied directly to principal are unusually powerful early in the loan, precisely because the balance is still high and generating the most interest. Paying an extra $200 a month in year one can cut years off a 30-year mortgage, because every dollar of extra principal payment stops compounding interest against you immediately. Refinancing to a shorter term does something similar structurally, but resets your amortization schedule and comes with its own closing costs to weigh.
See it on your own numbers
The shape of this curve depends on your rate and term — a higher rate stretches out the interest-heavy period, and a shorter term compresses it. Run your own numbers, including current property tax and insurance, in the mortgage calculator below.