What you can afford

Online calculators are helpful for finding a rough range, although they cannot know what else matters to your household. Travel, childcare, a career change or the first repair after moving in may all matter more to you than reaching the highest possible purchase price.

Why the monthly budget comes first

Test the mortgage payment at the rate you expect to start on and at a higher rate. Then add council tax, energy, water, insurance, broadband, service charge or estate charge where relevant, travel from the new address and a regular amount for maintenance.

Run that budget through an ordinary month and an expensive one. If it only works when nothing breaks and every discretionary cost disappears, it needs revisiting even if the payment sits within the lender's maximum.

Working out the cash needed up front

The deposit is only one part of the cash requirement. Allow for any property transaction tax, mortgage and valuation fees, conveyancing and searches, a survey, removals, initial insurance and the costs of making the home usable. Some of that money is spent before you know the purchase will complete.

A larger deposit can open lower loan-to-value bands and may improve the mortgage choices available. Whether that is worthwhile depends on the saving on the mortgage and the cash buffer you would give up.

How lenders assess what you may borrow

Income multiples are only a rough starting point. Lenders also look at committed spending, debts, dependants, the mortgage term, the stability and type of income, and their own stress tests. Two lenders can reach different answers from the same household.

A mortgage adviser can be useful where income is variable, self-employed, from several sources or recently changed. Going directly to a lender can also be reasonable for a simple case. The important questions are which lenders an adviser can consider, whether any deals are excluded, what the advice costs and how the adviser is paid.

Why the information in your credit file matters

The score shown by a credit-reference service is not the score a mortgage lender uses. Check the underlying reports for wrong addresses, accounts you do not recognise, missed payments and inconsistent details. Correcting an error can take time.

Registering to vote where eligible, paying commitments on time and keeping application details consistent can all help the file make sense. Do not take out credit simply to chase a consumer score, and do not make repeated mortgage applications to see what happens.

How to evidence your income and deposit

Lenders and conveyancers will want evidence of income, deposit and where the deposit came from. Savings built over time are usually easier to evidence than a large recent transfer. Family help, an inheritance, money held abroad, investments and a Lifetime ISA all have different paperwork.

If family money is involved, agree at the outset whether it is a gift or a loan. A lender may accept one and not the other, and the donor is likely to be asked for identity and source-of-funds evidence. See the gifted deposit guide before moving money around.

If part of the deposit is difficult to trace, avoid moving it through more accounts while the position is being checked. List each source and transfer, gather the statements or documents behind them, and ask the lender or conveyancer which part of the trail is still missing.

Should you buy now?

The best month to buy cannot be predicted reliably. A more useful test is whether you expect to stay long enough for the transaction and moving costs to make sense, have stable enough income for the commitment, can cope with a higher payment later, and still have a buffer after buying.

A plan that only works if house prices or interest rates move in one particular direction has little room for an outcome you did not expect.

Financial changes while a purchase is under way

A mortgage decision is based on the circumstances disclosed. New borrowing, missed payments or a material change in work or income can alter it. Tell the lender or adviser promptly if something changes; do not try to keep the application looking like an earlier version of your life.

The application also needs to be accurate when you first make it. Knowingly exaggerating income, hiding a debt or giving another false answer in order to obtain a mortgage can amount to fraud. At the very least it can cause the lender to reduce or withdraw the offer; depending on what happened, it can also have serious legal and financial consequences. Suspected fraud may be recorded with a fraud-prevention agency, making later applications for mortgages or other financial products more difficult. If you notice an honest mistake, tell the lender or adviser so it can be corrected rather than hoping it will not be checked.

Do not exchange contracts until your conveyancer is satisfied that the mortgage offer is available and its conditions have been met. Once you exchange, you are committed to the purchase. If a material change then causes the lender to withdraw and you cannot complete, your deposit may be at risk and the seller may be able to claim further losses. Keeping the gap between exchange and completion reasonably short reduces the time in which circumstances can change, although the conveyancers still need enough notice for the lender to release the mortgage funds.

What to check at this stage

• Set a monthly payment that works with your household budget, even if a lender is prepared to offer more.
• Allow for all the cash needed in addition to the deposit, including fees you may lose if the purchase falls through before exchange.
• Before increasing the deposit to obtain a lower mortgage rate, check how much emergency cash this would leave after completion.
• Check your full credit reports for errors several months before applying.
• Gather income and deposit evidence, including the history behind large transfers.
• Give complete and accurate information throughout the mortgage application, and correct an error as soon as you find it.
• Check whether the budget still works at a higher mortgage rate or after a fall in household income.
• Tell the lender or adviser about changes during the purchase, including new borrowing or a change in work or income.
• Before exchange, agree a completion date which keeps the gap manageable while giving the lender and conveyancers enough time to arrange the funds.