A mortgage deposit is a decision about how much money you commit to a home and what you want to keep afterwards. A lower borrowing percentage can help, but you also need enough cash for completion, moving, and the first unexpected bill.
The practical question is how much of your available money should go into the purchase, and what changes if you contribute a little more. That requires three separate figures: the price you agree on, the value the lender accepts, and the amount you need to borrow.
You can compare UK mortgage rates across different property values and deposit amounts to see how the results change. The displayed product is a starting point for discussion; you still need to check availability and eligibility.
Mortgage deposit at a glance: plan the contribution and the cash left over
- Calculate the borrowing needed after your contribution.
- Identify whether extra cash would cross a product’s loan-to-value limit.
- Keep purchase costs and your household reserve outside that calculation.
- Check the effect of a valuation below the agreed price.
- Compare realistic alternatives using the same mortgage term.
- Prepare evidence showing where the money comes from.
Mortgage deposit: Begin with the money you can actually commit
Start with accessible funds, rather than the total shown across every account. Then subtract money already needed for other purposes. A savings balance can look generous until legal work, a survey, moving costs and essential repairs are included.
Use three separate amounts in your plan: the contribution towards the purchase price, transaction costs, and money retained after completion. Give each a pound value. This makes it harder to count the same savings twice.
For example, £40,000 in accessible savings does not mean £40,000 is available towards the price. If you allocate £5,000 to buying and moving costs and retain £8,000, the contribution available is £27,000. These are planning figures, not estimates of what every household should spend or retain.
List the expenses relevant to your move using our guide to mortgage fees and buying costs. Obtain quotes where possible. A realistic allowance is more useful than a round number chosen to leave an attractive contribution.
What your mortgage deposit changes
Loan-to-value, or LTV, expresses the mortgage as a percentage of the property’s accepted value. Depending on the lender’s assessment, a larger contribution reduces borrowing and may open up different product options. It does not establish affordability or guarantee a lower rate.
The basic calculation is:
Mortgage amount ÷ property value × 100 = LTV.
For a standard purchase where the price and valuation match, borrowing £225,000 against a £250,000 home gives an LTV of 90%. The buyer contributes £25,000 towards the price, separately from costs.
Our explanation of loan-to-value covers the terminology. For this decision, focus on the next product limit you could realistically reach and the cash required to get there.
Test the threshold before adding more money
Imagine a £250,000 purchase with an equal lender valuation. The following calculations exclude fees added to the loan and make no assumptions about available rates.
| Contribution towards price | Mortgage required | Calculated LTV |
|---|---|---|
| £20,000 | £230,000 | 92% |
| £25,000 | £225,000 | 90% |
| £30,000 | £220,000 | 88% |
| £37,500 | £212,500 | 85% |
If a particular product has a maximum LTV of 90%, increasing the contribution from £20,000 to £25,000 moves the calculation within that limit. It still does not establish that the borrower meets its other requirements.
Adding another £5,000 reduces the loan to 88% LTV. However, if the next relevant product limit is 85%, that extra payment alone does not reach it. Under these assumptions, the buyer would need a total contribution of £37,500 to reach 85%.
This is why it helps to ask what an additional amount actually changes. It may reduce the loan without moving you into a different rate band. That can still be valuable, but it is a different benefit from gaining access to another product.
Do not round a figure down to fit a limit. A calculated 90.2% is above 90%. Ask the adviser to check the lender’s calculation, including its treatment of any financed fees.
Allow for a valuation below the purchase price
The seller’s agreed price is not a promise about the lender’s valuation. A lender may calculate borrowing against the lower of the purchase price and its accepted valuation. NatWest’s buyer guidance gives one example of this approach; check the applicable lender’s policy.
Return to the £250,000 purchase. The buyer intends to contribute £25,000 and borrow £225,000. Now assume the lender accepts a value of £240,000 and the chosen product permits a maximum of 90% LTV.
| Calculation | Result |
|---|---|
| Intended loan divided by accepted value | £225,000 ÷ £240,000 = 93.75% |
| Maximum loan at the assumed 90% limit | £240,000 × 90% = £216,000 |
| Cash needed towards the unchanged purchase price | £250,000 − £216,000 = £34,000 |
| Extra cash compared with the original plan | £34,000 − £25,000 = £9,000 |
The mortgage deposit needed for this assumed product has increased, even though the seller’s price has not changed. The £9,000 gap is additional to the buyer’s separately budgeted costs.
Notice another distinction. A £34,000 contribution would leave £24,000 of equity measured against the £240,000 valuation: £240,000 less £216,000 borrowed. The extra £10,000 paid above that valuation does not create additional equity on that basis.
RICS explains why a valuation below the agreed price can affect borrowing. A lower figure should prompt a review of the funding plan, rather than assuming the original mortgage will remain available. [12]
Review the purchase before filling a funding gap
An unexpected shortfall creates several questions. Could the price be renegotiated? Is there an alternative suitable product? Does the lender have a process for reviewing the valuation where there is supporting evidence? Would proceeding leave enough money for the household?
Treat these as separate possibilities. A seller does not have to reduce the price, and another lender need not accept a higher value. An adviser can explain mortgage options, while the conveyancer handles the legal position.
In the example, if the price instead fell to £240,000 and the buyer still contributed £25,000, the required loan would become £215,000. Against the same valuation, LTV would be approximately 89.58%. That arithmetic illustrates the effect of an agreed price change; it is not a predicted negotiation outcome.
Choose a mortgage deposit with room for ordinary life
Consider a second planning example. A buyer has £45,000 available for a £250,000 purchase. They allocate £5,000 to transaction costs and choose to keep an £8,000 household reserve.
That leaves £32,000 towards the price, requiring a £218,000 mortgage at 87.2% LTV if the valuation matches. Reaching 85% would require £37,500 towards the price. After the assumed costs, only £2,500 would remain.
The comparison is therefore between two complete plans. One retains £8,000; the other retains £2,500 and borrows £5,500 less. Don’t judge either figure without the household’s circumstances.
Write down what the reserve needs to cover: essential repairs, overlapping housing payments, irregular income or other known commitments. Separate unavoidable spending from improvements that could wait.
Ask for the mortgage comparison at both contribution levels. Then consider whether the difference in payments and product terms justifies committing the additional money. Don’t assume reaching a lower band must take priority over keeping accessible cash.
Check the source and timing of the funds
An agreed contribution needs to be available when the transaction requires it. Prepare an evidence trail for savings, sale proceeds or family support. Lenders and conveyancers may request different documents, so establish requirements early rather than moving money between accounts without keeping records.
Make a short funding schedule showing the amount, its source, when it becomes available and any conditions attached. If the purchase depends on another property sale, distinguish expected proceeds from money already received.
For family help, explain the arrangement accurately. A gift and a loan create different obligations. Do not describe repayable money as an unconditional gift merely to make the application appear simpler.
If any promised contribution changes, revisit the borrowing calculation before relying on the original product selection. A smaller amount might alter both the funding gap and the relevant LTV limit.
Keep affordability alongside the deposit decision
Income, expenditure, credit commitments and the property still matter to the lender’s assessment. Having enough cash to reach an LTV threshold does not, by itself, mean the required mortgage is affordable.
Use the residential affordability calculator as an initial planning step, then discuss the figures with an adviser. Bring your preferred contribution and a second realistic option, both with the cash reserve shown.
Modelling a contribution you cannot assemble, or a monthly payment that leaves the household stretched, has little value. Choose assumptions you could carry through to completion and keep them consistent when comparing results.
Before asking for a recommendation, prepare a one-page summary: agreed price, provisional valuation assumption, available contribution, separately funded costs, cash retained and borrowing required. Update it when a figure changes. This keeps a small change in one part of the purchase from disappearing inside an old calculation.
Questions worth asking before committing your savings
Is a 10% contribution always better than 9%?
It can cross a 90% LTV product limit where price and valuation match, but the available products and other criteria still determine the options. Compare what the extra contribution changes, including the money left after completion. A percentage alone cannot choose between two household budgets.
Can family support help reach the next band?
Potentially, if the contribution is acceptable to the lender and properly evidenced. The provider’s relationship to you and any repayment or ownership conditions may matter. Tell your adviser about the arrangement before including the money in your plan. Acceptance should be checked for the specific application.
Should I wait until I have a larger amount saved?
Compare two practical plans: buying with the funds available and waiting to save more. Include rent or other housing costs while waiting, the pace of saving and your likely cash position afterwards. Future prices and mortgage products are uncertain, so test both plans without relying on a forecast.
Discuss your mortgage deposit before selecting a product
Bring your figures to a Connect Mortgages adviser. Explain the amount you could contribute, the cash you want to retain and any uncertainty about the property’s value. The discussion can then address a purchase you could fund and borrowing that fits your circumstances.
Connect Mortgages is a trading style of Connect IFA Ltd, authorised and regulated by the Financial Conduct Authority, reference 441505. An arrangement fee applies and will be explained before you proceed. Connect may also receive lender commission.
Your home may be repossessed if you do not keep up repayments on your mortgage.
