Principal vs. Interest
Two payments of the same size can do very different amounts of work. Early in a mortgage, most of the money is rent on the borrowed balance; later, almost all of it is yours.
How each payment is split
Every period, interest is charged on the balance you still owe: balance × (annual rate ÷ periods per year). That comes out of the payment first, and whatever is left reduces the principal. Because the balance is largest at the start, the interest slice is largest then — and it shrinks every period as the balance falls, so the principal slice grows.
The crossover
The point where principal overtakes interest depends almost entirely on the rate. At a low rate it happens early; at a high rate on a 30-year loan it can be more than a decade in. Nothing goes wrong in either case — it's the same formula — but it explains why a balance seems to barely move in the early years.
Why the total is so large
Interest on a long mortgage often adds up to a substantial fraction of the amount borrowed — sometimes most of it again. Seeing it as a total rather than a monthly line item is what makes extra payments and shorter terms feel worth the trouble.
See your own split
Hearth charts principal versus interest for your loan, shows the period-by-period split in the amortization schedule, and tracks the equity-versus-balance curve — so you can see exactly which payment tips the balance in your favour.
Try it on your own numbers
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Open the calculatorFrequently asked questions
Why is most of my mortgage payment going to interest?
Interest is charged on the outstanding balance, which is at its highest when the loan is new. As the balance falls, the interest portion of each payment falls and the principal portion grows — the payment stays the same, the split changes.
When does more of the payment go to principal than interest?
It depends mainly on the interest rate. On a low-rate loan the crossover can come in the first few years; on a high-rate 30-year loan it can take well over a decade. The amortization schedule shows the exact period.
Do extra payments change the split?
Yes, in your favour. An extra payment goes entirely to principal, which lowers the interest charged on every payment after it — so more of each future payment reduces the balance.
Is mortgage interest calculated monthly or daily?
It varies by lender and market — many quote a rate compounded per payment period, some accrue daily. Hearth uses the standard per-period amortization used for monthly, biweekly and weekly schedules, which is close enough for planning; your lender's statement is authoritative.