Worked derivation
What a 15-year mortgage costs against a 30-year
The payment rises by about a third. The interest more than halves.
The same loan, two terms
36.7% more a month removes 55.6% of the interest.
$320,000.00 at 6.706%. Over 30 years the payment is $2,066.16 and the interest is $423,821.51. Over 15 years it is $2,823.91 and $188,303.66.
$757.75 more each month. $235,517.85 less interest in total.
Side by side
| 30 years | 15 years | |
|---|---|---|
| Monthly payment | $2,066.16 | $2,823.91 |
| Total interest | $423,821.51 | $188,303.66 |
| Total handed over | $743,821.51 | $508,303.66 |
| As a multiple of the amount borrowed | 2.32× | 1.59× |
| Principal repaid in year one | $3,439.16 | $12,816.91 |
| Month principal first beats interest | 237 | 57 |
Over thirty years the borrower hands over 2.32 times what they borrowed. Over fifteen, 1.59 times. Neither figure includes tax, insurance, fees or a deposit — it is the loan alone.
Both loans are charged the same interest in month one
This is the part that makes the rest make sense. On day one the balance is $320,000.00 on both loans and the rate is 6.706% on both. Interest is charged on the balance, so both are charged exactly $1,788.27.
30-year, month 1: $1,788.27 interest, $277.89 principal — 86.6% interest.
15-year, month 1: $1,788.27 interest, $1,035.64 principal — 63.3% interest.
The interest is identical. What differs is what is left over after it. A payment 36.7% larger retires 3.7 times as much principal, because the extra lands entirely on the balance rather than being split.
That compounds. A smaller balance next month means a smaller interest charge, which leaves more of the next payment for principal, and so on for the whole term. The shorter loan is not charged a better rate here — it simply spends less time owing money.
The term is the payment
Take the 30-year contract and pay the 15-year amount — $2,823.91 instead of $2,066.16, an extra $757.75 a month, with nothing else changed.
A real 15-year loan: 180 months, $188,303.66 of interest.
The 30-year, paid at the 15-year amount: 180 months, $188,303.66 of interest.
Identical, to the cent. At a fixed rate the term of a mortgage is not really a property of the product — it is the size of the payment. Two loans described very differently produce the same schedule when the same money goes in.
What genuinely differs is obligation. On the 15-year contract the larger payment is compulsory; on the 30-year it is not. That is a real difference between the two products, and it is not an arithmetic one — this page cannot tell you what it is worth to you.
A worked example you can check
Month one, on either loan. The balance is $320,000.00 and the nominal annual rate is 6.706%, so the interest is the balance times the rate divided by twelve:
320,000 × 6.706% ÷ 12 = 1788.2667 → $1,788.27
Subtract that from each payment and you have the principal each retires in month one: $277.89 and $1,035.64.
In a spreadsheet, =PMT(0.06706/12, 360, -320000) gives $2,066.16 and =PMT(0.06706/12, 180, -320000) gives $2,823.91. Multiply each by its number of payments, subtract $320,000.00, and you have the interest columns above to within the final payment's rounding. Our verification page walks through the same checks in more detail.
What this does not model
- The same rate on both terms. Lenders normally price a 15-year product below a 30-year one. This page holds the rate constant because it has no citable 15-year quote and will not invent one. That makes every gap here conservative — a genuinely lower 15-year rate would widen all of them.
- Anything but the loan. No property tax, insurance, HOA, closing costs, points or deposit. The figures are what the lender charges for the money, nothing else.
- Qualifying. A larger required payment is a larger income test, so the two terms are not always both available to the same borrower for the same house.
- What else the money could do. Whether a larger compulsory payment is worth making is not an arithmetic question and this page does not answer it.
The schedule is a US fixed-rate loan with interest charged monthly at the nominal annual rate divided by twelve — the convention a US lender's note describes, and the one the mortgage calculator on this site uses.
Common questions
- How much more is a 15-year mortgage payment?
- On $320,000.00 at 6.706%, $2,823.91 against $2,066.16 — $757.75 more a month, or 36.7% more. The interest over the life of the loan falls by 55.6%, from $423,821.51 to $188,303.66. The payment rises by about a third and the interest more than halves, because the money is borrowed for half as long.
- Why is the first month's interest identical on both?
- Because interest is charged on the balance, and on day one the balance and the rate are the same. Both loans are charged $1,788.27 of interest in month one. What differs is what is left over: $277.89 of principal on the 30-year against $1,035.64 on the 15-year — 3.7 times as much, from a payment only 36.7% larger.
- Is a 30-year paid at the 15-year payment amount the same as a 15-year loan?
- At the same interest rate, yes — identically, to the cent. Paying $2,823.91 on the 30-year contract clears it in 180 months having charged $188,303.66 of interest, which is exactly what the 15-year schedule produces. At a fixed rate the term is not a property of the product; it is the payment. What differs is whether the larger payment is compulsory.
- Do 15-year mortgages have lower interest rates?
- Usually, yes — lenders generally price a shorter term below a longer one. This page deliberately holds the rate constant across both, because it has no citable 15-year quote to use and will not invent one. Holding it constant isolates the effect of the term alone, and it makes the comparison conservative: a genuinely lower 15-year rate would widen every gap shown here.
- How much does the house end up costing?
- On these figures, 2.32 times the amount borrowed over 30 years — $743,821.51 handed over against $320,000.00 received. Over 15 years it is 1.59 times, or $508,303.66. Neither figure includes tax, insurance, fees or any deposit.
- When does more of the payment go to principal than interest?
- Month 237 on the 30-year — more than two-thirds of the way through the term. Month 57 on the 15-year, which is under five years. The crossover depends on the rate and the term, not on the amount borrowed.
Sources
- CFPB — What is an amortization schedule? — retrieved 2026-08-12
- Every figure on this page is produced at build time by the same engine the mortgage calculator runs, on $320,000.00 at 6.706%. That loan's 30-year payment of $2,066.16 matches calculator.net's published figure for the same inputs to the cent, which is the anchor everything here is measured against. No interest rate on this page is quoted from a lender; the same rate is applied to both terms deliberately, and the section above says why.
Written and maintained by Vikash Singh. Last verified 2026-08-17.