LTV Band Overpayment Calculator

If you have a lump sum sitting in a savings account and a remortgage coming up, the question is not "should I pay down some mortgage." It is "would this specific payment cross an LTV band threshold, and if so, how much does the cheaper rate save me on the entire remaining balance?" Our LTV band overpayment calculator settles it in a few seconds using live Bank of England band-average rates.

The leverage on a band-crossing payment is what makes this calculator worth running. A £6,000 payment that drops you from 81% LTV to 79% LTV does not just earn you the mortgage rate on £6,000. It can earn you a rate cut on every pound of the remaining balance for the entire next fix, with the specific gap depending on your lender's pricing at the time. On a larger mortgage that effect can run to a meaningful sum of saved interest, which may exceed what the same lump sum would earn in a savings account net of tax - though the result is sensitive to the rates available to you on the day. This page is general information and not personal financial advice; a regulated mortgage broker can model your specific case.

Contents

• The UK LTV bands and why they matter at remortgage
• How the calculator works
• Worked example: a £6k payment that cuts the rate on £250k
• Comparing against tax-adjusted savings rates
• When the calculator says stay in savings

The UK LTV bands and why they matter at remortgage

UK lenders do not price mortgages on a smooth curve. They price them in discrete bands, almost universally at 95%, 90%, 85%, 80%, 75%, and 60% loan-to-value. Crossing one of those thresholds at remortgage is the single biggest lever a typical homeowner has over their interest rate, and most people never think about it until a broker mentions it in passing.

The reason the bands exist is regulatory and operational. Lenders set risk pricing per band rather than per basis point of LTV, because the capital they have to hold against a loan steps up at those same thresholds. So a 79.9% LTV loan is typically priced like a 75-80% LTV loan, and an 80.1% LTV loan is priced like an 80-85% LTV loan. The gap between two adjacent bands varies by lender and market conditions, but it applies to the whole loan, not just the marginal pound that pushed you over the line - which is why the band step matters.

That makes the value of a lump-sum overpayment radically dependent on where you sit relative to the next band down. If you are at 91% LTV, paying £5,000 toward a £200,000 mortgage barely moves you and the cheaper rate does not arrive until you cross 90%. If you are at 81% LTV, the same £5,000 can put you under 80% and trigger a different rate on every penny of the remaining balance for the next two, three, five, or ten years depending on your fix. Our mortgage calculator helps with the headline payment maths; this one quantifies the band-step effect specifically.

How the calculator works

The calculator takes your lump sum, property value, current mortgage balance, remaining term, and the length of your next fix. It computes your current LTV, the LTV you would be at after the lump sum lands, and which band each falls into. It then pulls the Bank of England's published average rate for that fix length at each LTV band and uses the gap between them as the rate saving.

Two refinements matter. First, the savings comparison is tax-adjusted. You enter your savings rate (whatever your easy-access or fixed-rate cash account is paying) and your marginal income tax band. The calculator applies the Personal Savings Allowance (£1,000 basic rate, £500 higher, £0 additional) and taxes the rest at your marginal rate, giving you an effective post-tax savings yield to compare against the mortgage rate saving.

Second, the BoE averages are sector averages, not your specific lender's pricing. Real-world LTV-band gaps vary - some lenders set a flat rate above 75% and then drop sharply at 60% LTV, others spread it more evenly across all six bands. If you have actual quotes from a broker or a comparison site, plug them into the "Override BoE rates" panel and the calculator uses your real numbers instead.

The result shows a verdict (pay the lump sum, or keep it in savings), the net benefit in pounds over the fix length, the annualised return on the lump sum, the band jump, the monthly payment delta, and a year-by-year chart of net wealth under both paths. The CSV export is there if you want to paste it into a spreadsheet for a more detailed look. For the full-term version of this comparison, see our invest vs pay off mortgage calculator.

Worked example: a £6k payment that cuts the rate on £250k

Take a £250,000 mortgage against a £308,000 property. That is an 81.2% LTV, sitting in the 81-85% LTV band. The owner has a five-year fix coming up in a couple of months and £6,000 in a savings account paying 4.5% gross.

Pay the £6,000 onto the mortgage and the balance drops to £244,000 against the same £308,000 property. New LTV: 79.2%. That clears the 80% threshold and drops them into the 75-80% band. Assume - for illustration only - a 5-year fix gap of 0.2 percentage points between the two bands, so the rate falls from (say) 4.3% to 4.1%. Real-world gaps vary by lender, credit profile, and the day you apply.

Here is the thing most people miss. The 0.2pp rate cut does not just save 0.2% on £6,000. It saves 0.2% on £244,000 for five years. On those illustrative numbers that is roughly £488 a year in saved interest, or about £2,440 over the fix, plus the interest the £6,000 itself would have accrued on the mortgage (in the order of £1,300 at the new rate). The total modelled benefit of paying the lump sum on this example comes out around £3,700-£4,000 over the fix.

Compare that to leaving £6,000 in a 4.5% savings account for five years. At basic rate tax, after the £1,000 Personal Savings Allowance is exhausted, the post-tax yield is closer to 3.6% averaged across the period. On those assumptions that returns roughly £1,200-£1,400 net over the same five years. On this worked example the lump sum wins comfortably - but the worked example is illustrative, not a recommendation for any particular reader. Read should I overpay my mortgage for the wider opinion piece behind this maths.

Comparing against tax-adjusted savings rates

The savings side of the comparison is where most calculators get sloppy. They quote the gross savings rate and call it a day. In reality, savings interest above the Personal Savings Allowance is taxed at your marginal income tax rate, and the PSA itself is small enough that anyone with serious cash savings is hitting it.

The 2026-27 PSA bands are unchanged: £1,000 for basic-rate taxpayers, £500 for higher-rate, and zero for additional-rate. That means a higher-rate taxpayer with £20,000 in a 5% easy-access account is earning £1,000 gross interest, getting £500 of it tax-free, and paying 40% on the remaining £500 - an effective post-tax yield closer to 4% than 5%. An additional-rate taxpayer on the same setup is closer to 2.75% net.

Once you apply the marginal rate properly, the mortgage rate saving from a band-crossing overpayment will often beat holding the cash on the maths, because the rate gap on the whole balance can outweigh the post-tax interest on the lump sum alone. The exception is when the savings rate is high (around 5%+) and you are a basic-rate taxpayer with little enough cash that you are still under the £1,000 PSA - in that case the savings side can win on the numbers more often than people assume. The right call for you depends on your full circumstances and is not something this page can decide for you.

ISA wrappers change this entirely. Interest in a cash ISA is not taxed, so the effective yield is the gross yield, full stop. If you have spare ISA allowance and a competitive cash ISA paying close to the band-jump mortgage rate, the verdict can flip. The calculator does not currently model the ISA wrapper, so plug in your gross rate with "tax band: none" if all the savings are inside an ISA.

When the calculator says stay in savings

The verdict tilts toward savings in three specific scenarios. Recognising them stops you from making an irreversible overpayment when the maths says don't.

Your LTV is deep inside a band. If you are at 88% LTV against a 90%-to-85% band threshold, you would need to pay down a sizeable chunk of the balance just to start touching the next band. Until you cross 85%, the mortgage rate does not move. A lump sum that does not cross a band is just paying mortgage rate on the lump sum itself, which is fine but rarely better than holding the cash earning interest until you can deploy a bigger sum and cross properly.

You have a short fix left. Band-crossing rate savings compound over the length of the fix. A 0.2pp rate cut for two years is worth a quarter of the same cut for ten years. If you are in the last few months of an old fix that already includes early repayment charges, the saving window is too short to justify the lock-in. See our remortgage break-even calculator for the ERC version of this question.

Your post-tax savings rate is close to the mortgage rate. If a higher-rate taxpayer has cash in a 5%-paying ISA and a 4.5% mortgage, the savings yield is genuinely 5% net and the mortgage rate is 4.5%. Holding the cash can be mathematically better on those numbers, and the cash stays liquid in case life throws something unpleasant at the household budget. Liquidity has value, and mortgage overpayments are generally one-way - check your lender's specific terms on whether overpaid funds can be drawn back.

The right answer also depends on your wider financial position. Read our piece on UK mortgage types in 2026 for context on which fix length suits which household.