Savings
Simple payback and lifetime saving
- where
- net cost to the customer (£)
- installed cost (£)
- grant or funding (£)
- simple payback (years)
- annual bill saving (£)
- net lifetime saving (£)
- measure lifetime (years)
Explain this equation
Gives the simple payback and lifetime saving of an energy efficiency measure.
Any grant comes off the installed cost. Dividing what the customer pays by the yearly saving gives the years to get their money back. The saving over the lifetime of the measure, less the net cost, is the overall gain.
Payback is cost divided by yearly benefit.
Sense check: £8,000 against £459 a year pays back in about 17 years; over 30 years it saves about £5,800 net.
Watch out: simple payback ignores energy price changes, maintenance and borrowing costs. Part L uses 15 years simple payback as a feasibility test for some upgrades.
Works out how many years of bill savings repay the net cost of a measure, and what is left over across its life.
Enter your values to see the result.
Good to know
Grants change often. As of November 2026, ECO4 runs to 31 December 2026 and the Great British Insulation Scheme closed on 31 March 2026; check GOV.UK for the current Warm Homes funding before quoting. Simple payback ignores price inflation and discounting.
Common mistake
Quoting payback on the gross cost when the customer is getting funding, or the reverse.
Limits
No discounting, price escalation or maintenance. Treat as a rough guide only.
Sources
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow BS EN ISO 6946, BS 5250, PAS 2035, Building Regulations Part L and manufacturers’ data. Whole-house retrofit needs a qualified retrofit assessor and coordinator.