Your monthly mortgage payment is one of the largest financial commitments you'll make. Understanding exactly how it's calculated — and what each piece means — helps you compare loan offers, make smarter buying decisions, and understand how paying extra principal early in a loan saves enormous amounts of interest.
The formula for a fixed-rate monthly mortgage payment is:
M = P × [r(1+r)^n] / [(1+r)^n − 1]
Example: $350,000 loan at 7% for 30 years. Monthly rate = 7% ÷ 12 = 0.5833%. Payments = 360. M = $350,000 × [0.005833 × (1.005833)^360] / [(1.005833)^360 − 1] = $2,329/month (principal and interest only).
Most mortgage payments include four components, collectively called PITI:
A $350,000 mortgage at 7% with a 30-year term has a P&I payment of $2,329. Add $400/month property tax, $150/month insurance, and $175/month PMI, and the total monthly payment becomes approximately $3,054 — 31% higher than the bare P&I payment most people focus on.
With a fixed-rate mortgage, your monthly payment stays the same throughout the loan, but the split between principal and interest shifts significantly over time. In early years, most of your payment goes to interest. In later years, most goes to principal.
| Year | Annual Principal Paid | Annual Interest Paid | Remaining Balance |
|---|---|---|---|
| 1 | $3,502 | $24,446 | $346,498 |
| 5 | $4,222 | $23,726 | $330,116 |
| 10 | $5,917 | $22,031 | $305,553 |
| 15 | $8,300 | $19,648 | $271,836 |
| 20 | $11,638 | $16,310 | $225,115 |
| 25 | $16,319 | $11,629 | $151,948 |
| 30 | $22,889 | $5,059 | $0 |
Over 30 years at 7%, that $350,000 loan costs $488,444 in total — $138,444 in interest on top of the original principal. This is why rate differences of even 0.5% are worth fighting for.
Adding extra principal to your mortgage payment early in the loan saves disproportionately large amounts of future interest. On our $350,000 example: paying an extra $200/month from the start reduces the loan term from 30 years to approximately 25 years and saves over $68,000 in interest. Extra payments are most powerful early in the loan when the interest portion is largest.
The 30-year mortgage is more popular because of the lower payment, but the 15-year version is dramatically cheaper in total cost. On a $350,000 loan at 6.5% (rates are typically lower on 15-year loans):
Calculate your exact mortgage payment and see the full amortization schedule instantly.
Mortgage Calculator →Conventional lenders typically require a minimum 620 score, but the best rates go to borrowers with 740+. The difference between a 680 and 740 score on a $350,000 mortgage can be 0.5–0.75% in rate — translating to $100–$160/month difference in payment and $40,000–$60,000 over the loan's life. Improving your score before applying is one of the highest-return financial moves possible.
A common guideline: keep your total PITI payment below 28–30% of gross monthly income. At $90,000 annual income ($7,500/month), aim for a total mortgage payment under $2,100–$2,250. With current rates and typical taxes/insurance, that generally supports a purchase price of $280,000–$340,000 with a 10–20% down payment.
Each point costs 1% of the loan amount and typically reduces the rate by 0.25%. On a $350,000 loan, one point costs $3,500 and saves roughly $57/month. The break-even point is about 61 months (5 years). If you'll stay in the home longer than 5 years, buying points can make sense. If you might move sooner, it doesn't pay off.