How loan overpayments save you money
Most loans, mortgages and car finance agreements charge interest on whatever balance is still outstanding, then require a fixed monthly payment that covers that interest plus a bit of the balance itself. Early on, most of each payment goes on interest; later, once the balance is smaller, more of it goes on reducing what you owe.
An overpayment goes straight onto the balance on top of your normal payment. That lower balance means less interest is charged the following month, so a bigger share of every future payment reduces the debt rather than covering interest, which is why overpaying tends to save more than the overpayment amount itself once you add it all up over the life of the loan.
Lump sum vs regular overpayments
A lump sum reduces your balance immediately, in one go, for example putting a bonus or some savings straight onto the loan. A regular overpayment adds a smaller extra amount to every monthly payment from now on. Both approaches keep your required monthly payment the same and pay the loan off sooner rather than reducing what you owe each month. Use the toggle in the calculator above to compare either approach for your own loan.
Overpayment limits and early repayment charges
Before making a large overpayment, check your loan or mortgage terms. Many mortgage lenders allow overpayments of up to 10% of the outstanding balance each year without a charge, but anything above that, or paying the loan off entirely during a fixed deal, can trigger an early repayment charge, commonly a percentage of the amount over the limit. Personal loans and car finance agreements have their own rules, and some allow full early settlement with only a small, capped fee. This calculator estimates the interest and time you’d save; it can’t check what your specific lender would charge, so it’s worth confirming directly with them first.
Should you overpay or save the money instead?
Broadly, it comes down to comparing your loan’s interest rate against what you could realistically earn saving the same money elsewhere, after tax. A loan charging a higher rate than your savings would earn generally makes overpaying the better value choice, since the interest saved is certain, unlike investment returns. Most guidance also suggests building up an emergency fund first, since it’s usually much harder to get money back out of a loan once you’ve overpaid it than it is to dip into savings.
Example calculations
These worked examples come straight from the calculator above, so the figures match exactly what you’d see entering the same numbers yourself.
Personal loan, regular overpayment
£10,000 balance · 6% · £50/mo extra
- Interest saved
- £377
- Time saved
- 1 year 1 month
Car finance, lump sum
£12,000 balance · 7.9% · £2,000 lump sum
- Interest saved
- £668
- Time saved
- 9 months
Mortgage, staying within the 10% allowance
£200,000 balance · 4.5% · £200/mo extra
- Interest saved
- £36,281
- Time saved
- 6 years 1 month
Small loan, cleared early
£3,000 balance · 9.9% · £75/mo extra
- Interest saved
- £117
- Time saved
- 8 months
Frequently asked questions
How much can I save by overpaying my loan?
It depends on your balance, interest rate, remaining term, and how much extra you pay. As a general pattern, overpaying earlier in a loan saves more than overpaying later, because more of your balance is still outstanding and accruing interest. Enter your own figures in the calculator above for an exact estimate of the interest and time you'd save.
Does overpaying reduce my monthly payment or shorten my loan term?
This calculator assumes you keep paying the same monthly amount (plus any extra), so the loan is paid off sooner rather than your required monthly payment going down. Some lenders offer a choice between the two when you overpay: either keep the term the same and reduce future monthly payments, or keep the payments the same and clear the loan early. Clearing it early almost always saves more interest overall, since the balance falls faster.
What's the difference between a lump sum and a regular overpayment?
A lump sum is a one-off extra payment applied straight away, immediately reducing the balance interest is calculated on from that point. A regular overpayment is a smaller extra amount added to every monthly payment from now on. A lump sum of the same total size as a series of regular overpayments generally saves slightly more interest, because it reduces the balance sooner, but regular overpayments are often easier to commit to and adjust.
Will my lender charge me for overpaying?
Possibly, especially on fixed-rate mortgages and some personal loans. Many mortgage lenders let you overpay up to 10% of the outstanding balance each year without an early repayment charge, but anything above that, or clearing the loan entirely during a fixed deal, can trigger a fee. Always check your loan or mortgage terms, or ask your lender directly, before making a large overpayment; this calculator estimates the interest and time saved, but doesn't know about any charges your specific lender might apply.
Can I use this calculator for a mortgage as well as a personal loan?
Yes. Mortgages, personal loans and car finance agreements that charge interest on a reducing balance all work the same way mathematically, so the same calculation applies. Just enter your current outstanding balance, interest rate and remaining term, whichever type of loan it is.
How is loan interest actually calculated?
Most UK loans and mortgages charge interest daily or monthly on whatever balance is still outstanding, then add it to what you owe before your next payment is applied. Because your payment covers that interest first and reduces the balance with whatever's left over, paying more than required means less interest builds up the following month, which is why overpaying compounds into a bigger saving than the overpayment amount itself.
Should I overpay my loan or put the money into savings instead?
It usually comes down to comparing your loan's interest rate with the interest rate you'd earn saving the money instead, after tax. If your loan charges a higher rate than you could realistically earn saving, overpaying is typically the better value option, since the interest saved is guaranteed, while investment returns aren't. It's also worth keeping an emergency fund before prioritising overpayments, since it's usually harder to borrow the money back out of a loan once you've overpaid it.
Is there a limit to how much I can overpay?
Most lenders cap penalty-free overpayments at a percentage of your balance each year, commonly around 10% for mortgages, though it varies by lender and product. Personal loans sometimes allow full early settlement at any time, occasionally with a small settlement fee. Check your loan agreement or ask your lender for the exact limit that applies to you.
Does overpaying a loan affect my credit score?
Overpaying, and paying a loan off early, doesn't harm your credit score, and consistently making at least your required payments on time is generally positive for it. Closing a loan account entirely can occasionally cause a very small, temporary dip for some people, since it changes your mix of active credit, but this is a minor factor compared with maintaining a good payment history.
Methodology and assumptions
This calculator assumes:
- A standard fixed-payment, reducing-balance loan, the same structure used for most UK mortgages, personal loans and car finance agreements, with interest compounding monthly at a fixed rate for the rest of the term.
- Your interest rate stays the same for the remainder of the loan. If you’re on a fixed deal that’s due to end, or a variable or tracker rate, your real interest cost will change when the rate does.
- Overpayments are applied straight to the balance, with your lender charging no early repayment fee. Many lenders do charge one above a certain limit, commonly 10% of the balance a year for mortgages, so check your own terms first.
- With a regular monthly overpayment, your required payment stays the same amount higher every month from now on. With a lump sum, only the starting balance changes; your normal monthly payment is unaffected.
- All figures are rounded to the nearest penny.
Sources
This calculator is based on the standard loan amortization formula used across the lending industry, not a published government rule. General guidance referenced on this page:
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