Buying Before Selling: Stamp Duty, Funding and the Cost of Overlap

Buying your next home before selling your current one can keep a move on track. But on a £1 million purchase, it can also mean finding an extra £50,000 in Stamp Duty before the equity in your existing home is available.

A broken chain, a relocation or renovation work can make an overlap between homes attractive. The decision becomes harder when the deposit, tax and costs of two properties all need funding at once.

The starting point is a cash-flow plan: what must be paid before the sale, what finance is actually available, and how the borrowing will be repaid if the sale takes longer than expected.

Scope: the tax figures below concern residential purchases in England and Northern Ireland. Scotland uses Land and Buildings Transaction Tax; Wales uses Land Transaction Tax. Their rates and refund rules differ.

For the wider mortgage decision, visit our Residential Mortgages hub, which brings together guidance on moving home, affordability, porting and raising capital. This article focuses on the particular cash-flow problem created when the purchase happens first.

When buying first can make sense

Sometimes the overlap is a response to a problem: your buyer withdraws, a legal enquiry delays their purchase, or the seller of your next home will not extend the timetable. At other times it is a deliberate choice. Completing renovation work before moving, avoiding two moves with children, or securing a home close to a new job can all have practical value.

The benefit needs to be weighed against a measurable cost. Keeping control of your sale timetable may help you avoid accepting an immediate reduction in price, but that flexibility has a carrying cost. If extra interest, tax funding and household bills exceed the reduction you hoped to avoid, waiting for the preferred sale price may leave you worse off overall.

A useful decision therefore compares realistic alternatives: complete both transactions together, sell first and rent, buy first using available cash, or fund the overlap. The right answer depends on how much the timing matters to your household and what happens financially if the plan slips.

How much extra Stamp Duty could you need?

Current residential SDLT rates are 0%, 2%, 5%, 10% and 12% across successive price bands. Where the additional-property rules apply, each band is five percentage points higher. The uplift took effect on 31 October 2024; the current band thresholds took effect on 1 April 2025.

Calculated using HMRC's published residential bands. Assumes an individual buying a single freehold residential property, with no relief, exemption or non-resident surcharge. These are comparisons, not a personalised tax assessment. Source: HMRC residential SDLT rates.

Why a replacement home can attract the higher rates

Intending to live in the new property does not, by itself, prevent the surcharge. Keeping your previous home beyond the day of purchase can bring the transaction within the higher-rate rules.

Your conveyancer should check the full ownership picture, including overseas property, joint purchasers and a spouse or civil partner. Buying in one person's name does not necessarily avoid the rules. A separate 2% non-resident surcharge can also apply. Source: HMRC higher-rate guidance.

Selling the old main residence on or before the purchase can avoid the overlap surcharge where the replacement conditions are met. Those conditions matter even when you own other properties. Source: HMRC replacement-main-residence rules.

A possible refund is not completion money

A qualifying disposal of the previous main home within three years of buying the replacement may allow you to reclaim the higher-rate element. It is not a refund of the entire SDLT bill, and eligibility is not automatic. Source: HMRC refund guidance.

There is a separate claim deadline: for current sales, claim within 12 months of the later of the previous home's sale and the filing date of the SDLT return for the new home. Retaining an interest in the old home, or another reason for higher-rate treatment, can prevent a refund. Exceptional extensions to the three-year disposal period are limited. Source: HMRC refund conditions and deadlines.

The return and payment are normally due within 14 days of the effective date, usually completion. Your conveyancer will commonly require the tax funds as part of the completion arrangements. Allow for this before committing to the purchase. Source: HMRC filing and payment deadline.

A worked example: the gap before the sale

Imagine a buyer purchasing a £1 million home with a proposed £700,000 mortgage. Their existing home remains unsold and they have £250,000 in accessible cash.

• Purchase price less the proposed mortgage: £300,000.
• Higher-rate SDLT: £93,750.
• Cash required before fees and reserves: £393,750.
• Less accessible cash: £250,000.
• Initial shortfall: £143,750.

This is an illustrative funding calculation, not a mortgage offer. The shortfall grows once legal costs, finance charges and a reserve for the overlap are included. A possible £50,000 SDLT refund later does not close it today.

Do not count the exchange deposit twice: it normally forms part of the purchase price contribution. Do check when it must be available, because a facility released only at completion may not fund an earlier exchange deposit.

Equity and available cash are different figures

An existing home valued at £900,000 with a £300,000 mortgage has £600,000 of equity before sale costs. That does not mean £600,000 is available for the next purchase today. It becomes cash through a completed sale or approved borrowing, with each route having its own costs and conditions.

If borrowing against that property is part of the plan, the lender's valuation, permitted loan-to-value, existing mortgage and treatment of interest determine the usable advance. There may also be a need for the existing lender's consent or for its mortgage to be repaid. An estimate based only on the property's asking price can therefore overstate the money available.

Keep three figures separate in your planning: accessible cash now, the net advance available at completion, and the net proceeds expected from the eventual sale. Using future sale proceeds as though they were part of today's deposit is where an apparently comfortable transaction can develop a shortfall.

Which funding route fits the move?

Coordinate the sale and purchase

Simultaneous completion can release existing equity directly into the purchase. Selling first and renting temporarily is another option. Compare the extra moving and accommodation costs with the cost of financing an overlap, and consider the practical impact on your household.

Use a mortgage and available cash

Where accessible savings cover the purchase contribution and tax, a conventional mortgage may be enough. The lender still needs to assess the existing mortgage and other commitments. An anticipated sale should be disclosed; do not assume its mortgage payments will be excluded from affordability.

For borrowers with bonus income, company profits or uneven earnings, the way income is assessed can be just as significant as the property equity. A substantial asset base does not automatically satisfy a lender's affordability requirements. The adviser needs a clear picture of income, existing commitments and which debts will remain after the move.

Porting an existing mortgage product also needs to be checked against the actual sequence of events. Ask the lender whether the product can be retained when the new purchase precedes redemption of the old loan, what fresh assessment is required, and how any early-repayment charge or later refund would work. Do not budget for a refund until its conditions and timing have been confirmed.

Consider a short-term bridge

A bridge may fund a purchase ahead of a sale, subject to security, valuation and a credible repayment plan. Compare the cash actually released after retained interest and fees with the amount needed to complete. The headline facility amount can be higher than the usable advance.

Ask for the total repayment at your expected sale date and at later dates, including interest, arrangement fees, valuation, legal costs, exit charges and any minimum-interest period. Home-related bridging can be regulated; the adviser should confirm the status of the proposed facility. A bridge finances the transaction but does not remove its SDLT liability.

The security structure deserves as much attention as the rate. Where borrowing is secured over both homes, understand the conditions for releasing the property being sold and how much of the sale proceeds the lender requires. A sale may reduce the bridge without repaying it in full, leaving a balance that still needs an agreed exit.

Retained interest can reduce the cash released at the start, while interest added to the balance increases the amount eventually owed. Servicing interest monthly creates a different cash-flow requirement. Ask for a written illustration of the proposed arrangement so that upfront cash, monthly commitments and the final redemption figure are considered together.

Borrow against existing equity

A further advance, remortgage or second-charge loan may be considered, but a planned sale, affordability limits and early-repayment charges can make this unsuitable or expensive. Here, borrowing against equity means additional secured borrowing; it should not be confused with a later-life equity-release product.

Assess wider assets where relevant

For some clients, private-bank or investment-backed borrowing may be an option. Using a portfolio as collateral introduces another risk: falling values may lead to a demand for more security, repayment or the sale of investments. Compare that exposure with selling assets or using property finance.

Test the sale plan before exchange

A useful comparison includes a prompt sale, a six-month delay and a longer delay within the proposed facility's term. These are planning scenarios, not predictions or promises that a lender will offer an extension.

• Lower sale proceeds: deduct the existing mortgage, selling costs and any early-repayment charge. Then test a lower sale price.
• Longer overlap: include interest, mortgage payments, insurance, council tax, utilities and essential works.
• Loan maturity: establish what happens if the property remains unsold. Refinancing depends on future affordability, valuation and lender criteria.
• Change of plan: retaining or letting the old home alters the funding and tax assumptions. Rental income is not a guaranteed fallback.
• Cash reserve: keep enough accessible money for bills and contingencies after completion.

The three-year tax refund window is not a suitable repayment timetable for a short-term loan. The finance must work on its own contractual dates.

What does a slower sale do to the budget?

Suppose your combined additional property costs and serviced finance payments are £3,000 a month. A six-month overlap requires £18,000; twelve months requires £36,000. Those are hypothetical budget figures, not a bridging quotation. Interest added to a loan balance and charges outside the monthly budget must be accounted for separately.

A lower selling price can be more consequential still. On a planned £900,000 sale, a 5% reduction removes £45,000 from gross proceeds while the outstanding mortgage still has to be repaid. If the exit only works at the original asking price, review the borrowing amount, cash reserve or timing before proceeding.

What to establish before committing

Bring the financing and conveyancing advice together before exchange. An agreement in principle, an estate agent's valuation and an expected buyer are useful starting points, but each leaves matters outstanding. The available advance, the tax calculation and the completion arrangements need to fit the same transaction.

Ask for a clear schedule showing when the exchange deposit is due, when each facility releases funds, what your solicitor needs for completion and tax, and what must be repaid when the old property sells. Record who is handling the SDLT refund claim if one becomes available. This reduces the risk of a cost being omitted or the same money being allocated twice.

Buying before selling can be a considered way to manage a move. Its success depends on having sufficient funds at the right time and enough flexibility to cope with a slower sale. The strongest plan remains workable after a delay, rather than relying on every part of the chain completing exactly as expected.