The most common question borrowers ask when considering a HELOC is “how much can I borrow?” The answer depends primarily on the combined loan-to-value ratio (LTV), which is a calculation based on the property value, the existing mortgage balance, and the HELOC facility limit. In the UK, HELOC providers typically cap combined LTV at 85%, which means the total of the existing mortgage and the HELOC facility cannot exceed 85% of the property value.

This guide explains how the combined LTV calculation works for a HELOC, why it uses the full facility limit rather than the drawn amount, how much may be available at different property values, and how LTV affects the rate you are offered. A quick reference table provides estimates based on common property values and mortgage balances. All figures are illustrative only.

The combined LTV formula

The combined loan-to-value ratio for a HELOC is calculated using three numbers: the current value of the property, the outstanding balance on the existing mortgage, and the full HELOC facility limit being applied for. The formula is straightforward.

Combined LTV = (Existing mortgage balance + HELOC facility limit) divided by property value, multiplied by 100 to express as a percentage. For example, a property worth £350,000 with a £180,000 mortgage and a proposed HELOC facility of £75,000 would have a combined LTV of (£180,000 + £75,000) / £350,000 = 72.9%. This is within the typical 85% maximum, so the facility amount would be supportable from an LTV perspective (subject to affordability).

Working the formula in reverse gives the maximum HELOC facility at 85% combined LTV: (Property value x 0.85) minus existing mortgage balance. Using the same property: (£350,000 x 0.85) = £297,500, minus £180,000 mortgage = £117,500 maximum HELOC facility. The borrower in this example is applying for £75,000, which is well within the £117,500 maximum. The equity available calculator provides a quick estimate based on your own figures.

It is worth noting that the maximum facility calculated by the LTV formula is a theoretical ceiling. The actual amount available may be lower if the borrower’s income and existing commitments do not support the full amount under the lender’s affordability assessment. The guide to HELOC eligibility covers how the affordability assessment works.

Why the full facility limit is used, not the drawn amount

This is the single most important LTV nuance for HELOC borrowers, and it is different from how LTV works on a standard secured loan. On a standard loan, the LTV calculation uses the actual loan amount, because that is the full extent of the lender’s exposure. On a HELOC, the LTV calculation uses the full facility limit, even if the borrower only plans to draw a fraction of it.

The reason is straightforward: during the draw period (typically two to five years), the borrower can draw up to the full facility limit at any time. The lender needs to ensure that even at maximum exposure, the combined LTV remains within acceptable limits. A borrower who takes a £100,000 facility and draws £20,000 today could draw the remaining £80,000 tomorrow. The lender’s risk assessment must account for this possibility.

The practical implication is that requesting a larger facility than needed has a direct cost. A borrower who needs £50,000 but requests a £100,000 facility “just in case” is assessed at £100,000 for LTV purposes. This may push the combined LTV into a higher tier, which typically means a higher rate. If the extra £50,000 is likely to be needed, the higher facility may be worthwhile. If it is purely precautionary, the borrower may get a better rate by requesting only what is realistically needed and applying for additional borrowing later if circumstances change.

How much can you borrow? Quick reference table

The table below shows the maximum HELOC facility available at 85% combined LTV for different combinations of property value and existing mortgage balance. These figures are the LTV-based maximum only. The actual amount available will also depend on affordability, credit profile, and the provider’s own lending limits (typically up to £500,000 for HELOC facilities at the time of writing).

The table makes several things visible at a glance. First, the amount of available borrowing is heavily influenced by the existing mortgage balance. A borrower with a £200,000 property and a £150,000 mortgage has only £20,000 of headroom at 85% combined LTV, while a borrower with the same property value and a £75,000 mortgage has £95,000 of headroom. Second, the “not available” cells show where the existing mortgage already exceeds or is close to the 85% threshold, leaving no room for a HELOC. Third, higher property values create proportionally more headroom, which is why the right-hand columns show larger figures even at the same mortgage balance.

For a personalised estimate based on your own property value and mortgage balance, the equity available calculator provides a quick calculation. The LTV and equity calculator on the secured loans hub provides a more detailed breakdown including current LTV and available equity at different LTV tiers.

How LTV affects the rate

The combined LTV ratio is one of the most significant factors in the rate offered on a HELOC. Lower combined LTV means less risk for the lender (because there is a larger equity cushion protecting the lender’s position if the property needs to be sold), which translates to a lower rate for the borrower. Higher combined LTV means more risk and a higher rate.

The rate difference between LTV tiers can be substantial. As an illustrative guide, borrowers at below 60% combined LTV may access rates several percentage points lower than borrowers at 80% to 85% combined LTV. On a £40,000 facility, a rate difference of 3% translates to approximately £1,200 per year in additional interest cost. Over a fifteen-year term, the cumulative difference is significant. The guide to HELOC rates in the UK includes illustrative rate bands at different LTV tiers.

This creates a practical trade-off when deciding on the facility amount. A borrower who can achieve a lower combined LTV by requesting a smaller facility may qualify for a better rate, which can save more over the term than the “just in case” flexibility of a larger facility. Conversely, a borrower who needs the larger facility should factor the rate impact into their cost planning rather than being surprised by a higher rate at the offer stage.

Can you get a HELOC at 90% or 100% LTV?

At the time of writing, the maximum combined LTV for UK HELOC products is typically 85%. There are no UK HELOC products currently offering 90% or 100% combined LTV. This is a firm ceiling based on the risk appetite of the providers currently in the market, and it applies regardless of the borrower’s income, credit profile, or the property type.

For borrowers who need higher LTV lending, the alternatives are standard second charge mortgages from specialist providers, some of which offer combined LTV up to 90% or occasionally above. These are lump-sum products, not revolving facilities, so the drawdown flexibility of a HELOC is not available. But they may suit borrowers whose equity position does not support a HELOC at 85% combined LTV. The secured loans hub covers the full range of second charge mortgage options.

A 100% LTV product would mean borrowing the full value of the property with no equity cushion. This is not available on any mainstream UK secured lending product and carries extreme risk for both the borrower and the lender: any fall in property value would leave the borrower in negative equity.

How to improve your LTV position

If the combined LTV is too high for a HELOC, or if reducing the LTV would move the borrower into a more competitive rate tier, there are several practical steps that can help. None of these are instant solutions, but each can improve the position over time.

Reducing the existing mortgage balance through overpayments is the most direct route. Most mortgages allow overpayments of up to 10% of the outstanding balance per year without triggering early repayment charges. Each pound paid off the mortgage reduces the combined LTV by the same amount in the numerator of the calculation. For borrowers with available savings or surplus income, this can meaningfully improve the LTV position over twelve to twenty-four months.

Property value appreciation improves the LTV position without the borrower doing anything, but it is not controllable or predictable. Monitoring the local market and requesting an updated valuation when there is evidence of price growth can be worthwhile, particularly if the property was last valued during a softer market period. Home improvements that add genuine value to the property (extensions, additional bedrooms, kitchen or bathroom upgrades) can also increase the valuation, though the improvement must be reflected in the valuation to affect the LTV calculation. An automated valuation model (AVM) may not capture recent improvements; a physical RICS valuation may be needed in this case.

Requesting a smaller HELOC facility is the simplest adjustment. Because the LTV calculation uses the full facility limit, a smaller facility directly reduces the combined LTV. A borrower who needs £40,000 but was considering a £60,000 facility for contingency purposes may find that the £40,000 facility qualifies for a materially better rate, making it the more cost-effective choice overall.

Frequently asked questions

Does the combined LTV change during the HELOC term?

The underlying components change, but the facility limit remains fixed. The existing mortgage balance reduces over time through regular payments, which improves the combined LTV. Property values may rise or fall, which also affects the ratio. However, the HELOC facility limit, which is the maximum the borrower could draw, stays the same throughout the draw period. This means the “current” combined LTV is a snapshot that changes gradually as the mortgage is paid down and property values move.

Lenders do not routinely recalculate combined LTV during the HELOC term. The LTV assessment is done at the point of application and is used to set the rate and facility limit. A subsequent improvement in LTV (through mortgage reduction or property appreciation) does not automatically result in a rate reduction or an increased facility limit on the existing HELOC.

Can I increase my HELOC facility later if my LTV improves?

Not automatically. The facility limit is set at the outset and does not change during the term. If the borrower’s LTV position improves significantly (for example, through substantial mortgage reduction or property value growth) and they want a larger facility, this would typically require a new application. A new application means a new valuation, a new affordability assessment, new fees, and new legal work.

Whether this is worthwhile depends on how much additional borrowing is needed and whether the improved LTV qualifies for a better rate that offsets the cost of the new application. The guide to refinancing a HELOC covers the options for changing the facility terms.

What if my property value falls after I take the HELOC?

The facility terms are agreed at the outset and are not automatically revised if the property value changes after completion. A fall in property value does not trigger an immediate change to the HELOC rate, facility limit, or repayment terms. The borrower continues making repayments as agreed.

However, a fall in property value could affect future options. If the borrower wants to refinance the HELOC at the end of the draw period, the new LTV calculation would use the current (lower) property value, which may result in a less competitive rate or a smaller facility than the original. In extreme cases, if the property value has fallen enough that the combined LTV now exceeds the lender’s maximum, refinancing to a new HELOC may not be possible, and the borrower would continue on the existing repayment terms.

Is the LTV calculation different for a HELOC vs a standard secured loan?

Yes, in one important respect. For a standard secured loan (lump-sum second charge mortgage), the combined LTV uses the actual loan amount, because the borrower receives the full amount at completion and cannot draw more. For a HELOC, the combined LTV uses the full facility limit, because the borrower could draw up to that amount at any point during the draw period.

This means a borrower comparing a £50,000 standard secured loan with a £80,000 HELOC (of which they plan to draw £50,000) is assessed at different combined LTV levels for each product. The HELOC LTV will be higher because the calculation includes the full £80,000, not the £50,000 intended draw. This can affect the rate offered and, in some cases, whether the application is accepted. The guide to home equity loan vs HELOC covers the structural differences between the two products.

Does equity from home improvements count toward the LTV calculation?

Only if the improvement is reflected in the property valuation. The LTV calculation uses the property value as assessed by the lender, not the amount the borrower has spent on improvements. An extension that costs £40,000 to build may add £60,000 to the property value (improving the LTV) or it may add only £25,000 (improving the LTV less than expected). The amount added depends on the type of improvement, the quality of the work, and the local market.

The valuation method also matters. Most UK HELOC providers use an automated valuation model (AVM), which estimates the property value using comparable sales data and property records. An AVM may not capture recent improvements because it relies on historical data rather than a physical inspection. If the borrower has carried out significant improvements and wants them reflected in the valuation, a physical RICS valuation may be needed. This is at the borrower’s expense and is not guaranteed to produce a higher figure. The guide to HELOC eligibility covers the valuation process.

This article is for informational purposes only and does not constitute financial advice. Your home may be at risk if you do not keep up repayments on a mortgage or other debt secured against it. All LTV calculations and borrowing amounts shown are illustrative and based on a typical 85% combined LTV maximum. Actual amounts depend on the provider’s lending criteria, affordability assessment, and property valuation. Actual outcomes will depend on your individual circumstances.