Sizu When a loan payment feels too high, the easy fix is to ask for a longer term. The monthly payment drops, so it feels like a bargain. The cost is hidden in the total.
Here is one example, worked out. The loan is $200,000 at 6% a year, fixed, repaid monthly. The rate is an example, not an offer.
Step 1: the monthly payment
A repayment loan has a payment that stays the same each month. With monthly rate i (6% ÷ 12 = 0.5%) and n monthly payments, the formula is:
payment = loan × i ÷ (1 − (1 + i)^−n)
This is the one step you do with a calculator. The results, rounded to the cent:
- 25 years (300 payments): $1,288.60 a month
- 35 years (420 payments): $1,140.38 a month
The longer loan saves $1,288.60 − $1,140.38 = $148.22 a month. That is real relief if money is tight.
Step 2: the total you pay back
Multiply the payment by the number of payments:
- 25 years: $1,288.60 × 300 = $386,581 in total, so $186,581 is interest.
- 35 years: $1,140.38 × 420 = $478,959 in total, so $278,959 is interest.
(Amounts rounded to the nearest dollar.)
The extra ten years adds about $92,400 of interest. You pay roughly $148 less a month, and about $92,400 more overall. Put differently, each $1 a month you save today costs you about $620 over the extra ten years.
Step 3: why early payments barely touch the loan
Interest is charged on what you still owe. In month one you owe the full $200,000, so one month of interest is:
$200,000 × 0.5% = $1,000
That is the same on both loans. Whatever is left of the payment reduces the loan:
- 25 years: $1,288.60 − $1,000 = $288.60 off the loan
- 35 years: $1,140.38 − $1,000 = $140.38 off the loan
On the 35-year loan only about 12% of the first payment shrinks the debt, so the balance falls slowly at first. A slow start means more months paying interest on a large balance, which is where the extra $92,400 comes from.
Step 4: choosing with the numbers in view
A longer term is not always wrong. If the shorter payment is genuinely unaffordable, a lower payment is the safer choice. Some people take the long term and then pay extra when they can. Because overpayments reduce the balance, they cut the interest that is charged afterwards.
Useful questions before you sign:
- What is the payment on a 5-year-shorter term, and could I manage it?
- What is the total paid, not just the monthly figure?
- Can I pay extra later without a penalty? (Check the terms.)
Step 5: what overpaying does
Suppose you take the 35-year loan but pay the 25-year payment of $1,288.60 anyway. That is $148.22 above the minimum each month. Every extra dollar goes straight to the balance, so next month’s interest is a little smaller, and the extra share keeps growing. The loan then ends well before year 35. You keep the freedom to drop back to $1,140.38 in a hard month, which the 25-year contract would not allow. The price of that flexibility is that it only works if you really do pay the extra.
To see the exact saving for your own loan, change one number at a time (term, then extra payment) and compare total interest each time. The cost of a loan is the thing to compare, since the monthly figure alone hides it.
Step 6: check any quote the same way
Whenever you are shown a monthly figure, do the two multiplications yourself. Take the payment, multiply by the number of months, and subtract the amount borrowed. The result is the interest, and it is the number that lets you compare two offers on equal terms. If an offer also has an arrangement fee, add it to the total as well. A cheaper-looking monthly figure on a longer term can easily be the more expensive loan, as the example shows. Do the sum before you decide, not after.
A final sense check: the average interest per month over 25 years is $186,581 ÷ 300 = about $622, and over 35 years $278,959 ÷ 420 = about $664. Both are well below the $1,000 of month one, because the balance falls over time. The longer loan is the one that stays near that $1,000 level for longer, which is the whole story in one line.
Rule of thumb
Compare total paid, not the monthly payment. Shorter term: higher payment, much less interest. Longer term: lower payment, much more interest.
Try it with your own numbers
The Loan & Mortgage Calculator gives the monthly payment, total paid, total interest and the full schedule, with an overpayment what-if. The LTV & Equity tool covers deposit and equity. They belong to The Mortgage & Loan Math Workout, Book 4 of Math That Pays.
This is arithmetic for planning, not financial advice, and no lender or product is recommended. Real loans may include fees, and rates vary.