The 20/4/10 rule
Popularised in the US but useful here: put at least 20% down, run finance for no more than 4 years, and keep the total cost of car ownership (finance, insurance, fuel, tax, servicing) under 10% of your gross income.
It's more conservative than most UK drivers are used to, but if the numbers work under this rule, they'll work under any lender's affordability check.
The 15% net-income rule
Simpler version: your car finance monthly payment shouldn't exceed 15% of your take-home pay. If your net monthly is £2,400, that's £360/month on finance. Add insurance and fuel and you're at real-world car cost.
Most UK specialist lenders will decline anything comfortably above 20% net-income affordability, so 15% keeps you well within safe territory.
The one-third-of-savings deposit rule
If you're deposit-shopping, put down at most a third of your accessible savings. Cars are depreciating assets — the money is gone the moment you drive off the forecourt. Keep two-thirds liquid for the boring but essential (insurance renewal, tyres, emergencies).
The soft-search sanity check
Before falling in love with a specific car, run a soft-search quote for the amount you're considering. Lenders' affordability models factor in your existing outgoings — so a car that looks affordable on your salary might not be, once your rent, credit card and childcare payments are visible.
A soft-search quote takes 2 minutes and never touches your credit file. It's the fastest way to know your real budget.
