How much interest does a 15-year mortgage save compared to a 30-year mortgage?

On a 300,000 loan at 6.5% over 30 years versus 6.0% over 15 years, the shorter option saves approximately 227,000 in total interest. The exact figure depends on loan size, the gap between the two rates, and the rate environment overall. Higher rates magnify the absolute saving on the shorter term because more of each payment goes to interest in early years. Savings scale roughly proportionally with loan size, so a 600,000 loan at the same rates produces savings of about 454,000. The 15 vs 30 year mortgage calculator runs exact figures for any loan amount and rate pair.

Why is the 15-year mortgage rate usually lower than the 30-year rate?

Lenders price longer-term loans with a premium because they carry more risk over a longer horizon. A 30-year mortgage locks the lender into a fixed return for three decades, during which rates could rise, the borrower could default, or inflation could erode the real value of repayments. A shorter term carries those risks for half the time, so lenders accept a lower rate. The gap typically ranges from 0.25 to 0.75 percentage points, depending on the rate environment and the lender.

Can a 30-year mortgage be paid off in 15 years through overpayments?

In many markets, yes. Overpaying a 30-year mortgage at the level of a 15-year payment will clear the loan in roughly 15 years and capture most of the interest saving. The catch is the rate gap. Because 15-year mortgages typically carry a lower rate, paying a 30-year mortgage at the 15-year payment level still costs more than simply taking the 15-year option in the first place. The upside of the overpayment approach is flexibility: the higher payment is voluntary rather than contractual. Some lenders cap annual overpayments or apply early repayment charges, so the loan terms matter.

Is a 15-year mortgage worth the higher monthly payment?

It depends on three things: how comfortably the higher payment fits the budget, what alternative uses the cashflow has, and how long the borrower expects to hold the loan. When the higher payment fits well within affordability and no higher-returning use exists for the difference, the interest saving on the 15-year option is substantial. When the cashflow difference could fund retirement contributions, emergency reserves, or other priorities, the trade-off becomes closer. Running both versions through the calculator and lining them up against other financial priorities is the practical way to decide.

How does inflation affect the 15 vs 30 year mortgage decision?

Inflation erodes the real value of fixed mortgage payments over time. A 30-year loan benefits more from this effect because later payments, made in money worth less than today's money, stretch further across a longer schedule. In environments where inflation runs above the mortgage rate, the real cost of a long-term loan can be meaningfully lower than the nominal figures suggest. In low-inflation environments, the effect is small. The comparison in the worked example uses nominal numbers, which slightly overstates the real cost of the longer term in inflationary periods.

15 vs 30 Year Mortgage: Real-Numbers Comparison

Take a 300,000 loan at typical fixed rates. Over 30 years at 6.5%, the borrower pays roughly 382,600 in interest. Over 15 years at 6.0%, the same loan costs about 155,700 in interest. The shorter term saves around 227,000, but it costs an extra 635 every month for fifteen years to get there. That is the whole argument, sitting in three numbers.

Most coverage of this topic glosses over how big the gap actually is. This guide shows the formula, runs the worked example end to end, and walks through where each term tends to suit different borrowers. The 15 vs 30 year mortgage calculator handles any loan size and rate pair, but seeing the maths once makes the output much easier to interpret. The framing is country-neutral, so the same logic holds whether the loan is in pounds, dollars, euros, or anything else.

What is the trade-off between 15-year and 30-year mortgages?

The choice is between repaying a home loan over a shorter or longer fixed schedule. A 30-year mortgage spreads principal across 360 monthly payments. A 15-year mortgage spreads the same principal across 180. Same debt, half the time, roughly double the speed of pay-down.

Because interest accrues each month on whatever balance is still outstanding, faster pay-down compounds in the borrower's favour. Less time owing money equals less interest, and the gap is much larger than most people expect. Lenders typically offer a lower headline rate on shorter terms too, which widens the gap further still. The cost is monthly: the shorter loan requires a higher payment, and that payment is contractual, not optional.

Why this trade-off matters

For most households, a mortgage is the single largest debt they will ever carry. The Organisation for Economic Co-operation and Development tracks household debt to disposable income across member countries, and mortgages dominate that ratio in nearly every developed economy. Choosing between terms shifts hundreds of thousands of units of currency across a borrower's lifetime, and a meaningful amount of monthly cashflow flexibility either way.

The decision is not purely mathematical. A lower monthly payment can fund retirement contributions, build emergency reserves, or absorb a job loss without missing a housing payment. A higher payment locks more capital into the home but kills the loan faster. Inflation matters too: a long fixed-rate loan repays its later instalments in money that has lost purchasing power, which quietly shifts the breakeven in favour of longer terms when inflation runs above the loan rate.

None of these factors change which term has lower lifetime interest. They change whether the lifetime interest figure is the right thing to optimise for.

How the calculation works

Each monthly payment comes from the standard fixed-payment amortisation formula. It produces a constant monthly figure that fully repays the loan over the chosen term. The comparison runs the formula twice, once for each term, then reports the difference in monthly payment, total amount paid, and total interest.

M = P * [r * (1 + r)^n] / [(1 + r)^n - 1]

Where:

M = the fixed monthly payment
P = the principal, the amount borrowed
r = the monthly interest rate (annual rate divided by 12)
n = total number of monthly payments (180 for 15 years, 360 for 30)

Total interest is the monthly payment multiplied by the number of payments, minus the principal. The calculation uses two different rates (one per term), not a single rate applied across both, because that is how lenders actually price these products.

A worked example with real numbers

Numbers below use currency-neutral units. Maria is comparing two offers on a 300,000 loan:

30-year term at 6.5% fixed
15-year term at 6.0% fixed

For the 30-year option, the monthly rate is 6.5% divided by 12, or about 0.005417. The number of payments is 360. Plugging into the formula:

M = 300,000 * [0.005417 * (1.005417)^360] / [(1.005417)^360 - 1]
M = roughly 1,896 per month

Total paid is 1,896 times 360, or about 682,600. Subtract the 300,000 principal and the total interest comes to roughly 382,600.

For the 15-year option, the monthly rate is 6.0% divided by 12, or 0.005. The number of payments is 180.

M = 300,000 * [0.005 * (1.005)^180] / [(1.005)^180 - 1]
M = roughly 2,532 per month

Total paid is 2,532 times 180, or about 455,700. Subtract the principal and the total interest comes to roughly 155,700.

Putting them side by side:

Monthly payment: about 635 more on the 15-year option
Total interest: about 227,000 less on the 15-year option
Total amount paid: about 227,000 less on the 15-year option

The shorter term costs Maria 635 more every month, but saves her roughly 227,000 across the life of the loan. That is the whole trade in one line, and the numbers scale roughly proportionally for any loan size at similar rates. Double the loan to 600,000 at the same rates, and the savings double to about 454,000.

How to use the calculator

The 15 vs 30 year mortgage calculator takes three inputs: loan amount, the 30-year rate, and the 15-year rate. The two rates are entered separately because lenders almost always price them differently. Outputs include each monthly payment, total paid, and the total interest saved by going shorter.

Read the result as three numbers together, not one. The monthly payment difference shows the cashflow cost of accelerating. The total interest difference shows the lifetime saving. The ratio between them indicates how efficiently extra monthly outlay converts to long-term savings, and it grows as the shorter-term rate falls below the longer-term one. If the two rates are very close, the shorter term still saves substantial interest, but the case for it weakens.

Common scenarios

Stable income with room to spare

A borrower whose income sits comfortably above the higher monthly payment usually finds the shorter term efficient. The 635 monthly difference in the worked example converts to roughly 227,000 in interest savings, which is hard to match anywhere else. The cleanest case is when the higher payment sits within roughly 25% to 30% of gross monthly income, leaving genuine headroom for everything else. Pairing this with a quick check on a mortgage affordability calculator can confirm the higher payment fits before committing.

Variable income or thin reserves

A self-employed borrower, or anyone with limited emergency savings, often gets more value from the longer term. The lower required payment can be voluntarily exceeded in good months and dropped back to the minimum in lean ones. Many lenders allow overpayments without penalty, so the longer term can replicate part of the shorter-term saving while keeping the lower payment as a fallback. For households without an emergency reserve in place, an emergency fund calculator sits naturally alongside the mortgage decision as the second number to size.

Strong returns available elsewhere

If the 635 monthly difference could earn a return higher than the mortgage rate, the longer term becomes more competitive. Invested at a 7% annual return, 635 a month compounds to roughly 201,000 over fifteen years. That is real money, though still slightly below the 227,000 saved by paying the loan down directly, and the comparison ignores tax on investment returns. The outcome here depends heavily on tax wrappers and on whether the borrower will actually invest the difference rather than spend it.

Plan to move within a few years

If the home is unlikely to be held to maturity, the lifetime interest comparison matters far less. What matters is interest paid over the holding period and the equity built. On the 30-year option above, only about 19,000 of principal has been repaid after five years. On the 15-year version, the same five years builds substantially more equity, because more of each payment goes to principal from day one. For shorter holding periods, that equity build often matters more than the lifetime interest gap.

Frequent oversights

Comparing terms without comparing rates. 15-year and 30-year loans rarely carry the same rate. Using one rate for both understates the saving on the shorter option, sometimes badly.
Ignoring opportunity cost. Interest saved by paying the loan faster is real, but so is the return foregone by not investing that cashflow elsewhere. Both numbers exist; only one usually gets mentioned.
Stretching the monthly payment too far. A shorter-term payment that swallows most of disposable income leaves no buffer for shocks. Interest savings do not help a borrower who falls behind.
Forgetting the overpayment option. Voluntarily overpaying a longer-term loan can shorten the effective term substantially while preserving the lower required payment as a safety net.
Treating total interest as the only metric. Total interest is large in absolute terms, but it is spread over decades. Monthly affordability and resilience matter just as much.

The mortgage term decision rarely sits alone. A few related tools tend to feed into it:

Mortgage affordability calculator — pressure-test whether the higher 15-year payment leaves enough room for everything else.
Emergency fund calculator — size the buffer that sits alongside any mortgage commitment, especially a stretched one.
Compound interest calculator — model what the 635 monthly difference could grow to if invested instead of accelerating the loan.

Sources and methodology

The amortisation formula used here and in the linked calculator is the standard fixed-payment mortgage equation documented in finance textbooks worldwide. The worked example numbers have been computed and verified to within rounding.

Background data on household mortgage debt and housing market structure draw on:

These global sources provide cross-country context on mortgage market structure and long-term housing finance trends without anchoring to any single jurisdiction's tax or regulatory environment.

The bottom line

The choice between a 15-year and a 30-year mortgage is not a single right answer. It is a deliberate trade between monthly cashflow and lifetime interest, with secondary effects from inflation, opportunity cost, and household resilience. The worked example sizes that trade: 635 more per month buys roughly 227,000 in interest savings. Whether that exchange looks attractive depends on how the monthly difference compares to other uses of the cash, and on how stable the income behind the payment is. Running the numbers explicitly turns the decision from a feeling into a comparison, and that is usually all that is needed to settle it.