Mortgage Calculator

What the Monthly Payment Actually Covers

The monthly payment calculated here covers only principal (reducing the loan balance) and interest (the cost of borrowing). Real housing costs usually include more: property taxes, home insurance, mortgage insurance where lenders require it, and service or community charges on some properties. What each adds varies widely by market. In markets where taxes and insurance are collected alongside the mortgage payment, the all-in monthly figure commonly runs well above the principal-and-interest number this calculator shows. The principal-and-interest figure is the comparable core; the rest is local.

How Amortisation Works

Standard amortising mortgages have fixed monthly payments, but the split between principal and interest shifts over time. Early payments are mostly interest because the loan balance is large; late payments are mostly principal because the balance has shrunk. For a typical 30-year mortgage at 6%, the first year sees about 17% of each payment go to principal, while the 30th year sees more than 90% going to principal. The calculator returns the fixed monthly payment but does not break out the shifting interest-principal split; an amortisation schedule tool does that.

What the Rate Does to Total Cost

A 400,000 loan at 4% over 30 years costs 1,910 monthly and 287,478 in total interest. The same loan at 7% costs 2,661 monthly and 558,036 in total interest. The 3-percentage-point difference adds 751 to the monthly payment and 270,558 to lifetime interest. Even a 0.25% difference changes total interest on a 400,000 loan by roughly 21,000 to 25,000 over 30 years at rates between 4% and 8%, with the larger figure at higher rate levels. For scale, choosing a 15-year term over a 30-year on the same loan at 6% moves total interest by 255,776, a different order of magnitude from any quote spread. The two comparisons answer different questions.

Term Length Trade-Off

A standard comparison, on a 400,000 loan at 6%: the 30-year term costs 2,398 monthly with 463,353 in total interest, while the 15-year term costs 3,375 monthly with 207,577 in total interest: 255,776 less over the life of the loan, at a monthly payment roughly 40% higher at typical rates (more at lower rates). The shorter term concentrates the same debt into fewer, larger payments, so far fewer months accrue interest. The higher payment needs more income to qualify; the total cost of ownership is what it buys.

The levers at the sample figures

At the sample figures used on this page (a 400,000 home, 80,000 down, 6.5%, 30 years), one percentage point on the rate moves the payment by about 215 a month; shortening the term by five years adds about 138; a 10% lower home price removes about 253; and a 10% smaller down payment adds about 51. The four levers use different units, so the figures are not a ranking; a percentage point of rate is not comparable to a tenth of the price. What they show is the scale of each decision as it is actually faced: rate quotes differ by fractions of a point, while price and term move in much larger steps. These magnitudes scale with loan size, so they shift proportionally in other currencies or at other price points.

Worked Example for a Typical Home Purchase

Home price 400,000; down payment 80,000 (20%); rate 6.5%; term 30 years. Loan amount: 320,000. Monthly payment: 2,022.62. Total paid over 30 years: 728,142. Total interest: 408,142, more than the original loan amount. Loan-to-value: 80%. In a market where property tax and insurance are billed monthly (say 3,500 and 1,200 a year respectively, with no mortgage insurance because of the 20% down payment), the true monthly housing cost comes to about 2,414 against the calculated 2,022.62 of principal and interest. The all-in figure includes the recurring costs a household actually pays each month; the principal-and-interest figure omits them.

Why the Down Payment Share Matters

In many markets, lenders require mortgage insurance when the down payment falls below a threshold, often around 20% of the price. Where a charge of, say, 1% of the loan per year applies, a 320,000 loan carries about 267 a month on top of the payment, and the rules for when the charge ends vary by market and lender. A larger down payment also lowers the loan-to-value ratio, which is the figure lenders price against; the calculator shows it directly so the threshold effects are visible.

The Extra Payment Effect

On the 400,000-at-6% mortgage, adding one-twelfth of the payment to every monthly instalment (the smoothed version of one extra payment a year) shortens the term from 30 years to roughly 24 and a half and saves about 98,000 in interest. The exact figure depends on how the extra lands: a single full extra payment once a year saves about 95,000, while a true biweekly half-payment schedule saves about 99,000, because each variant reaches the principal at a different point. Extra payments punch above their weight because they reduce principal early, when the balance and therefore the interest cost are highest. This calculator does not model extra payments; the Early Mortgage Payoff and Mortgage Overpayment calculators handle that path properly. Approximating an overpayment here by shortening the term changes the contractual payment rather than the balance path, so it understates the saving.

Refinancing Considerations

Refinancing to a lower rate reduces the monthly payment and total interest, at the price of the refinance costs. The break-even is the number of months until the monthly saving covers those costs. On the 400,000 mortgage, moving from 7% to 6% saves about 263 a month; with 4,000 of refinance costs the break-even lands at about 15 months. How long the owner stays past that point determines how much of the saving is actually collected. The calculator handles the payment math for any rate-and-term combination, so the two scenarios can be compared directly.

What the Calculator Does Not Include

The figure excludes property taxes, home insurance, mortgage insurance, service or community charges, maintenance, utilities, and the purchase and completion fees on the transaction itself. It also excludes prepayment conditions some lenders apply, any tax treatment of mortgage interest where that exists, and (because the model is fixed-rate only) any payment change from a variable or adjustable rate. Each of these varies by market; the calculation is the portable core.

Where the Numbers Commonly Mislead

The patterns that most often mislead are budgeting on principal and interest alone, comparing terms on monthly payment without looking at total interest, overlooking mortgage insurance when the down payment is under the local threshold, and treating purchase fees as negligible when they are material on most transactions. Each becomes visible once the corresponding comparison is run through the calculator.