EPC Calculator: What Each Upgrade Does to Your Rating

How EPC Ratings Actually Work

An EPC rates a home from 1 to 100 and puts it in a band:

For an existing home the assessment is RdSAP 10, the reduced-data version of the government's Standard Assessment Procedure. It works out what the home would cost to heat, light and supply with hot water for a standard household, at fixed prices set in BRE's specification: mains gas at 3.48p a kWh plus a £120 standing charge, electricity at 13.19p, and solar generation valued at 13.19p. The higher that cost for the size of the home, the lower the score (the formula divides by the floor area plus 45 sq m, so a small home scores a little lower at the same cost per sq m). Today's energy prices and your own use don't come into it.

That's why some upgrades earn more points than their bill savings would suggest. Solar panels earn a lot, because every kWh they generate counts at the full electricity price. A heat pump earns some of its points simply because the gas standing charge (£120 at RdSAP prices) goes once the home has no gas. A loft top-up earns little, because there's not much heat left to save once there's 100mm up there. In England and Wales an EPC is valid for 10 years, and the report lists recommended measures with the rating after each; gov.uk's landlord guidance says those ratings are cumulative, assuming the measures are done in the order listed.

Scotland is changing. New regulations come into force on 31 October 2026: new-style EPCs carry an Energy Cost Rating, an updated version of today's rating, alongside a Heat Retention Rating for the fabric, and are valid for 5 years instead of 10. Existing EPCs can still be used for a sale or let until 31 October 2027. Our calculator follows the RdSAP 10 method behind today's ratings in England and Wales.

How to Get from D to C

The calculator starts from a 1950s semi of 90 sq m with unfilled cavity walls, 100mm in the loft, older double glazing and a condensing gas boiler, scoring 62. On our estimates, each upgrade on its own adds:

C starts at 69. The cheapest way there on our estimates: air source heat pump, about £4,700, for a score of about 70. The heat pump cost is after the £7,500 Boiler Upgrade Scheme grant, which is England and Wales only (Scotland has its own grant of up to £7,500). A home that starts near the top of D needs only a point or two, so check the score on your certificate rather than the band.

How to Get from E to C

The same semi scoring 47, the middle of E, needs 22 points to reach C. The cheapest way on our estimates: cavity wall insulation and solar panels (4kWp), about £8,600, for about 71. A home with solid walls, open chimneys or an older boiler has more to gain, and the calculator shows what each is worth when you set them.

Grants for EPC Upgrades

• Boiler Upgrade Scheme: £7,500 towards a heat pump in England and Wales if you own the home.
• Warm Homes: Local Grant: England only, for homes rated D to G with a household income usually of £36,000 a year or less.
• ECO4: through energy suppliers until 31 December 2026, for households on certain benefits (homeowners rated D to G, private tenants E to G with the owner's permission) and for social housing rated E to G.
• Scotland: Home Energy Scotland offers a grant of up to £7,500 towards a heat pump (£9,000 for rural and island homes), with an optional interest-free loan, and grants for insulation.
• Wales: Nest offers free improvements to eligible households.
• Northern Ireland: the Boiler Upgrade Scheme doesn't apply, so add £7,500 back to the calculator's heat pump cost.

Our insulation grants in England and heat pump grants pages have the details.

Landlord EPC Requirements

A privately rented home in England and Wales has to be at least E. Under the current rules you don't have to spend more than £3,500 including VAT; if that doesn't get you to E, you make the improvements you can for that amount and register an exemption. The maximum fine is £5,000 per property now; under the new rules it rises to £30,000 per property per breach.

The government has confirmed a single compliance date of 1 October 2030 and a cost cap of £10,000, and spending on qualifying measures installed since 1 October 2025 counts towards it. Other funding counts towards the cap, but not a Boiler Upgrade Scheme grant. Homes valued below £100,000 get a lower cap, 10% of the value.

The standard is set against new EPC metrics, not today's score. A rental needs a new EPC showing C or above on a fabric performance metric (the government lists measures like cavity wall, loft and underfloor insulation, draught proofing and double glazing) and on either a heating system or a smart readiness metric. A rental rated C or above on an EPC lodged before 1 October 2029 counts as compliant until that EPC expires. So the points in our calculator are for today's rating: a route that relies on solar panels may reach C now without meeting the fabric standard in 2030.

What to Do Next

Find your certificate on gov.uk's find an energy certificate service (England, Wales and Northern Ireland; Scotland has its own), put its score and floor area into the calculator, and set the walls, loft and heating to match. Its recommended measures, and an assessor's new rating once you've done the work, are what count. For what each measure saves on bills, use our insulation savings calculator.