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Pick the year you bought. This replays real 15-year and 30-year mortgage rates and stock market returns, with the lower payment's difference invested, to the latest month.
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Both borrow the same and spend the same each month. Whichever pays less that month invests the difference.
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This 15 vs 30 year mortgage calculator replays the choice with real rates. Pick the UK or the US and the year you bought (any January from 2000), and it follows two mortgages on the same home to the latest month: a shorter one with bigger payments, and a longer one with smaller payments and the difference invested.
Both paths spend the same each month. On the 30-year mortgage, the gap between the two payments goes into the stock market (or savings) every month. Once the 15-year mortgage is paid off, that path invests the whole of what the 30-year one still pays. Each ends as investments minus the mortgage still owed; the home is the same on both, so it cancels out. You can also compare 10 or 20 years against 25, 30 or 35.
In the US, each term takes Freddie Mac's average rate for that month: the 15-year fixed is usually about half a point to three quarters of a point lower than the 30-year. In the UK, lenders charge the same rate whatever the term, so both take the average new two-year fix, refixed every two years; only the length changes. Unless you type your own, the home is the average UK home or typical US home in the month you buy, less a 25% deposit or 20% down. Returns are tax-free with no fund fees, as in an ISA or a Roth IRA; the US mortgage interest deduction is left out.
These use the calculator's starting figures for one UK and one US case, and are refreshed when the data updates.
Had you taken a 30-year mortgage of £131,727 in January 2015 and put the £361 a month it saved into the stock market, instead of a 15-year one, by August 2026 you'd be £67,000 better off with the 30-year mortgage.
Had you taken a 30-year mortgage of $151,210 in January 2015 and put the $350 a month it saved into the stock market, instead of a 15-year one, by August 2026 you'd be $56,000 better off with the 30-year mortgage.
It depends on what the market did. The 15-year mortgage pays less interest, at a lower rate, and is paid off sooner; the 30-year leaves money every month to invest. Pick a year above: when stock returns beat the 30-year rate, investing the difference came out ahead, and when they didn't, the shorter mortgage did.
The table shows the interest paid on each so far. Over the full terms, a 15-year mortgage typically pays well under half the interest of a 30-year one on the same loan, because the balance falls faster and the US rate is lower. The calculator counts what the 30-year path does with the money it didn't pay, which a plain interest comparison leaves out.
Yes: the mortgage term. UK lenders offer the same rate whatever the term, so a 15-year term just means bigger payments and less interest, and a 30 or 35-year term smaller payments. Choose UK above to compare them, with each two-year fix at the average rate of the day.
Pick "Savings" above. The difference earns real savings rates instead of stock returns: the 3-month Treasury bill yield in the US, the Bank of England average one-year fixed-rate bond rate in the UK. Savings usually earn less than the mortgage costs, so the shorter mortgage tends to win.
No. Most US households take the standard deduction and get nothing from it. If you itemise, the 30-year mortgage's extra interest cost you less after tax than shown, which would tilt the result towards it.