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Loan overpayment: shorten the term or lower the payment? The numbers

When you overpay a loan, the lender asks whether to shorten the term or reduce the monthly payment. On a $300,000 mortgage, $200 a month extra saves about $103,000 one way and $42,000 the other. Worked examples, three traps, and how to check your own loan.

Overpaying a loan almost always saves money, but how much depends on one setting most people never look at: whether the extra goes to shortening the term or lowering the payment. Shortening the term saves roughly two to three times more interest. Lowering the payment buys breathing room instead. Both are legitimate choices, as long as you make them on purpose.

You can run your own numbers in the free loan overpayment calculator. Below is what it shows on typical loans, and why the results come out the way they do.

The starting point

A typical fixed-rate mortgage: $300,000 over 30 years at 6.5%, equal monthly payments.

  • Monthly payment: $1,896
  • Total interest over the full term: $382,600

That last number is the one to keep in mind. Over thirty years you pay the bank more in interest than you borrowed. Nobody is cheating here: that is simply what a 6.5% rate does when it runs for 360 months.

Option one: shorten the term

You pay $200 a month extra, and the lender keeps the payment the same and shortens the loan.

  • Paid off after 23 years and 1 month instead of 30
  • Total interest: $279,200
  • Saved: about $103,400

For $200 a month you buy almost seven years without a mortgage payment.

Option two: lower the payment

Same $200 a month, but the lender recalculates the payment and keeps the original end date.

  • After the first year the payment drops from $1,896 to about $1,881, and keeps falling a little every time you overpay
  • The loan still ends in 30 years
  • Total interest saved: about $42,500

Same money in, less than half the savings out.

Why the difference is so big

Interest is a charge for time. Every month the lender charges interest on whatever balance is left. Shortening the term takes months away from the lender: seven years of interest that never gets charged. Lowering the payment leaves all 360 months in place and only makes the balance a bit smaller in each of them.

There is a second effect. When the payment drops, the principal part of each payment drops too, so the balance falls more slowly than it would have. Part of your overpayment is effectively undone by the smaller payments that follow it.

A one-off lump sum

Overpayments do not have to be monthly. A single $10,000 paid at the start of the same mortgage:

  • Shortening the term: loan ends 2 years and 9 months early, interest saved about $53,900
  • Lowering the payment: payment drops by about $63 a month, interest saved about $12,800

The ratio is even more lopsided than with monthly overpayments, because a lump sum paid early has the whole remaining term to work.

Personal loans and car loans work the same way

The mechanics do not change with the size of the loan. A $15,000 personal loan over 5 years at 12%:

  • Normal payment: $334 a month, total interest $5,020
  • $100 a month extra, shortening the term: paid off after 3 years and 7 months, interest $3,500, saved $1,520
  • Same $100, lowering the payment: saved about $970

Smaller numbers, same pattern. With personal loans there is one more question to ask first: whether the lender charges an early repayment fee. More on that below.

When lowering the payment is the right call

Maximum savings are not always the goal. Lowering the payment makes sense when:

  • The payment genuinely strains your budget. A loan paid off at the cost of your emergency fund turns the first car repair into credit card debt at 20% or more, which is far more expensive than the mortgage.
  • Your income is irregular. A lower required payment lowers the bar you have to clear in a bad month. That resilience costs money, and sometimes it is worth it.
  • You plan to sell the property within a few years. A shorter term only pays off if you are still holding the loan when the shortened years would have run.

In every other case shortening the term wins, and it is not close.

Three traps lenders do not advertise

The default is not always the better option. Some lenders apply extra payments to lower the payment, or to prepay future installments, unless you say otherwise. If you have never chosen consciously, check what your lender does. You might have been overpaying in the weaker mode for years.

The extra has to go to principal. A payment sent without instructions can be treated as paying next month's installment early. Then nothing is saved at all, you have just paid on time a little sooner. Most lenders have a separate "extra principal" field or a written instruction for this.

Early repayment fees. Many personal loans, car loans and fixed-rate mortgages allow a fee for paying early, often limited to the first few years or capped at a percentage of what you overpay. Read the contract before the first overpayment: a fee can wipe out the gain from the early ones.

What this does not say

It does not say overpaying is always the best use of spare money. At 6.5%, an overpayment is a guaranteed, risk-free 6.5% return. That is good. But if you carry a credit card balance at 22%, pay that off first; the order in which to pay off debts matters more than any single overpayment. And if you do not yet have an emergency fund, build that first. A paid-down mortgage and an empty account is how the next big expense comes back as expensive debt.

It also does not say you should overpay as much as possible. An overpayment you abandon after three months because it squeezed the budget too hard does less than a steady $100 kept up for ten years.

How to check your own loan

You need four numbers from your loan statement: remaining balance, interest rate, months left and current payment. Put them into the overpayment calculator and it shows both options side by side: how many months each one cuts and how much interest each one saves.

In Ordiarion the same calculation sits next to the rest of your budget, so you can see whether the extra $200 actually fits in your month before you commit to it.