The formula
Cost of buying = outlay − what the car is worth at the end
Where it comes from
With a lease you pay to use and hand it back at the end. Buying, you pay to own, and at the end you hold an asset you can sell. So comparing payments alone is always biased towards leasing: a lease payment includes depreciation, insurance and servicing, and a loan payment only the car. Here the residual value is deducted from the cost of buying, which is what puts the two on the same footing.
How to work it out by hand
- Add the deposit and every lease payment: that is the leasing cost
- Work out the loan payment on the financed amount over the term
- Add deposit, payments and buying costs
- Subtract what the car will be worth at the end: that is the real cost of buying
What is worth knowing
One important piece is missing on both sides and is worth handling manually: a lease usually includes fully comprehensive insurance, servicing and road tax, and buying does not. If the lease bundles three thousand a year of those, add them to the buying side for a fair comparison. And the residual value is an estimate: an electric car and a diesel do not depreciate alike, and a good deal of the answer rides on that.