Principal — what you owe and how it falls

Principal is the amount you borrowed. Every mortgage payment chips away at it, but the split between principal and interest changes dramatically over 30 years.

Updated August 2026

When you take out a $400,000 mortgage, that $400,000 is your principal. Every month you make a payment, part of it goes to the lender as interest — their fee for lending you the money — and the rest actually reduces what you owe. That reduction is the principal portion.

In the early years, almost every dollar goes to interest. By the final years, almost every dollar retires debt. This gradual shift is called amortization, and the chart below shows what it looks like over a full 30-year loan.

$400,000 mortgage at 7% — 30 years

Outstanding principal Cumulative interest paid

Real number examples

Month 1 — almost all interest

Loan: $400,000 at 7% on a 30-year term. Monthly P&I payment: $2,661. Month 1 interest: $400,000 × (0.07 ÷ 12) = $2,333. Principal reduction: $2,661 − $2,333 = $328. Balance remaining: $399,672.

Year 10 — momentum building

After 120 payments totalling $319,320, you have paid approximately $286,500 in interest and reduced your balance by only $32,820 — to roughly $367,180. Your monthly principal portion has grown to about $628.

Year 20 — the tipping point is past

Balance is now approximately $278,000. Monthly principal: ~$1,200. Monthly interest: ~$1,461. At this point more than 45% of each payment reduces the debt.

Total cost over 30 years

Total payments: $2,661 × 360 = $957,960. Principal repaid: $400,000. Total interest paid: $557,960 — nearly 40% more than the original loan.

Frequently asked questions

What is the difference between principal and interest?

Principal is the amount you actually borrowed and still owe — the debt itself. Interest is the lender's charge for lending it to you. Every monthly payment is divided between the two: the interest portion is calculated on the current balance (so it is highest at the start), and the rest reduces the principal. As the balance falls, the interest portion shrinks and the principal portion grows — that is amortization.

Does every payment reduce my principal?

Yes, every standard mortgage payment includes some principal reduction, even in the first month. On a $400,000 loan at 7% on a 30-year term, your first monthly principal-and-interest payment of $2,661 includes only about $328 of principal and $2,333 of interest. By year 15 that split is closer to $780 principal and $1,881 interest. By year 25 it flips: about $1,600 principal and $1,061 interest per month.

How can I pay down principal faster?

Make extra payments directed specifically at principal (tell your servicer it is principal-only). Even one extra payment a year on a 30-year mortgage can cut the loan life by 4–5 years. You can also refinance to a shorter term — a 15-year mortgage forces faster principal reduction because the payoff horizon is compressed. Bi-weekly payments (paying half your monthly payment every two weeks) add one extra full payment per year automatically.

What is an interest-only loan?

An interest-only mortgage requires no principal repayment during the interest-only period, typically 5–10 years. Your payment only covers interest, so the balance never moves. After the interest-only period ends, the loan recasts — you then owe the full original balance amortized over the remaining term, which causes a significant payment jump. Interest-only loans made sense when home prices rose reliably; they carry more risk in flat or declining markets.

How does principal work differently in Canada?

The concept of principal is identical in Canada — it is the outstanding debt. The key difference is how interest is calculated. Canadian mortgages compound semi-annually by law, not monthly. This means the effective monthly rate is (1 + annual rate ÷ 2)^(1/6) − 1 rather than annual rate ÷ 12. On a $500,000 loan at 5% over 25 years, the Canadian formula yields a payment of $2,908.02 vs the US formula's $2,922.95 — about $15/month less, adding up to roughly $4,500 over the amortization.

See your own principal schedule

The full amortization table — every month's principal and interest — is available in both calculators.