Compare the same period
Choose a realistic occupation period, then list rent, bills and any agreed rental costs for that period. For a purchase, include acquisition costs, service charges, maintenance, financing if any and eventual selling costs. Use the same currency and time period for both.
Do not treat a mortgage payment as directly equivalent to rent. A repayment mortgage pays interest and reduces the capital owed; an interest-only mortgage pays interest while the borrowed capital still needs to be repaid, normally by the end of the term. Ask an authorised mortgage adviser to compare the options.
For illustration only, rent of £3,000 a month for 36 months is £108,000 before bills or other costs. That is a rental cost, not the amount a family would necessarily save by buying. A purchase comparison must include its own transaction and ownership costs and the uncertain amount recovered on sale.
Further reading: MoneyHelper: buying and moving costs · MoneyHelper: repayment and interest-only mortgages
Show what remains uncertain
A purchase has an unknown future sale price and sale date. Test more than one scenario, including a longer period on the market or a change in the property’s value. Do not assume that rent saved will equal a gain on resale.
Allow for major works, repairs and periods when the property is empty. For a leasehold flat, seek the service charge accounts and details of proposed works rather than relying solely on the current monthly figure.
Further reading: GOV.UK: service charges
Keep cash committed separate from cost
For a cash purchase, the price becomes capital tied up in the property. A sale may release some or all of it; some owners may also be able to borrow against the property, subject to lender terms and eligibility. The difference between purchase and sale prices is uncertain; neither the full price nor an assumed gain is a monthly cost.
For a mortgage, compare the deposit, fees, interest and remaining loan at the assumed sale date with the proposed rental payments. Ask an authorised mortgage adviser to explain the figures and what would change if the home were sold earlier.
Further reading: MoneyHelper: applying for a mortgage
Consider flexibility and commitments
A rental agreement and a purchase have different commitments and exit arrangements. Ask the relevant adviser or letting provider about the actual tenancy terms; ask your conveyancer about the lease and sale process for a purchase.
A planned course or job can change. Consider who makes decisions if the person using the flat leaves early, and whether the owner would want to retain, sell or potentially let the home.
Where Rivermark can help
Rivermark can discuss a search for a home to buy and compare property information with your brief. We agree the work and fees before starting. This comparison does not offer a rental search, a letting service or a prediction of returns.
A solicitor, surveyor and tax or finance adviser can assess the commitments and figures for your circumstances.
Official guidance checked 5 November 2026. Confirm the current position and how it applies to your circumstances with the relevant adviser.