Remortgage Calculator

When your fixed-rate mortgage deal ends, you are automatically moved to your lender’s standard variable rate (SVR), which is typically 3–5 percentage points higher than the initial deal. On a £250,000 balance, that jump can add £400–£800 to your monthly payment. A remortgage calculator shows you exactly how much you could save by switching to a new rate before the SVR kicks in.

What is remortgaging?

Remortgaging means replacing your existing mortgage with a new one – either with the same lender (a product transfer) or a different one. The goal is to secure a lower interest rate, change your repayment terms, or release built-up equity from your property.

You are not moving house. The new mortgage pays off the old one, and you continue living in the same property under updated terms.

In the UK, roughly 1.5–2 million homeowners remortgage each year. The average switch saves between £2,000 and £4,000 over the initial fixed period, according to industry data from UK Finance.

How does a remortgage calculator work?

A remortgage calculator compares your current mortgage against a potential new deal. You provide a few key numbers, and it estimates the difference in monthly payments and total cost over the remaining term.

Inputs you need:

• Outstanding mortgage balance – the amount you still owe
• Remaining term – years left on your mortgage
• Current interest rate – the rate on your existing deal
• New interest rate – the rate you are considering switching to
• Property value – used to calculate your loan-to-value (LTV) ratio

The calculator returns:

• Current monthly payment vs. new monthly payment
• Monthly saving (or cost increase)
• Total interest saved over the remaining term
• Whether the switch makes financial sense after fees

The calculation uses the standard amortisation formula:

M = P × [r(1 + r)^n] / [(1 + r)^n – 1]

Where P is the principal (outstanding balance), r is the monthly interest rate, and n is the number of remaining monthly payments.

Why remortgage your home?

The most common reasons homeowners switch their mortgage:

• Better interest rate. Even a 0.5% reduction on a £200,000 balance saves roughly £50 per month or £3,000 over a 5-year fix.
• Avoid the SVR trap. Standard variable rates average around 7.5–8% in 2026. Competitive fixed deals start from roughly 4–4.5%, depending on your LTV.
• Change your term. Shorten the term to pay off the mortgage faster, or extend it to reduce monthly outgoings.
• Release equity. Borrow against the increased value of your home for renovations, a deposit on another property, or debt consolidation.
• Switch from interest-only to repayment. Build equity each month instead of only covering the interest.

What types of remortgage deals are available?

Lenders offer several product structures. Your choice depends on your risk appetite and how long you plan to stay in the property.

Fixed-rate deals remain the most popular choice. In 2026, approximately 75% of remortgage customers opt for a 2-year or 5-year fix.

When is the best time to remortgage?

Start looking 3–6 months before your current deal expires. Most lenders let you secure a rate up to six months in advance. If market rates rise in the interim, you keep the locked-in rate. If they fall, many lenders allow you to switch to the lower rate before completion.

Key timing signals:

• Your fixed or discounted period is ending within the next 6 months
• You have already moved to the SVR
• Your LTV has dropped below 75% or 60%, unlocking better rate tiers
• Interest rates are trending downward, making a tracker worth considering

What does remortgaging cost?

Switching is not free. Factor in these expenses to calculate the true saving:

• Arrangement fee (product fee): £500–£2,000. Some lenders let you add this to the loan, though you then pay interest on it.
• Valuation fee: £150–£1,500, depending on property value. Many remortgage deals include a free valuation.
• Legal fees: £300–£1,000. Lenders frequently offer free legal work as part of the package.
• Early repayment charge (ERC): 1–5% of the outstanding balance if you leave your current deal early. On a £200,000 mortgage, a 3% ERC costs £6,000 – often more than the potential saving.
• Broker fee: £0–£500, depending on the broker. Many brokers are free to the borrower, receiving commission from the lender instead.

The calculator above factors in these costs to give you a net saving figure rather than a misleading gross number.

How to compare remortgage offers

Look beyond the headline rate. The true cost of a deal depends on several variables:

1. Annual percentage rate of charge (APRC). This includes fees and reflects the total cost over the full mortgage term. Use it to compare like-for-like.
2. Total fee burden. A 4.2% rate with zero fees may cost less over a 2-year fix than a 4.0% rate with a £1,500 arrangement fee.
3. ERC flexibility. Some products allow overpayments of up to 10% per year without penalty. Others lock you in rigidly.
4. Speed of process. A product transfer with your existing lender typically completes in 2–4 weeks. A full remortgage with a new lender takes 4–8 weeks.

Interest rates and eligibility criteria change frequently. Always verify current offers directly with lenders or through an FCA-regulated mortgage broker.

LTV ratio and why it matters

Your loan-to-value ratio – the outstanding mortgage divided by the property’s current value – directly affects the rates available to you. Lower LTV unlocks cheaper deals.

If your property has increased in value since you took out the mortgage, your LTV may have dropped naturally. A new valuation – which the remortgage lender arranges – could place you in a lower band and save you thousands.

Remortgage vs. product transfer: which is better?

A product transfer is simpler: you stay with your current lender, choose a new deal from their range, and avoid most of the legal and valuation costs. The process takes days rather than weeks.

A full remortgage to a new lender takes more effort but can yield a significantly lower rate, especially if your current lender is not competitive. Research from L&C Mortgages shows that borrowers who shop the full market rather than accepting the first offer from their existing lender save an average of £500–£1,000 per year.

Use the calculator to model both scenarios – staying with your lender at the rate they have quoted versus switching to the best market rate – and compare the net saving after all fees.