What is an EPC potential score — and should you care?

What is the potential score?

The potential rating is the EPC band the property could theoretically reach if all the “cost-effective” improvements recommended in the certificate were carried out. The assessor calculates this based on the property's current features and the expected benefit of each improvement.

So a property currently rated E might show a potential rating of C — meaning the assessor believes it's possible to reach C with the recommended work.

The key word is “cost-effective.” The methodology only includes improvements that are deemed to pay back within a reasonable timeframe. More expensive improvements — like external solid wall insulation — may not be included in the potential calculation even if they would significantly boost the rating.

Why the gap between current and potential matters

A large gap is an opportunity

If a property is rated E with a potential of B, that's a significant gap — but it suggests the property is improvable. The improvements may be expensive, but you're buying a property with genuine upside in terms of energy efficiency and running costs.

Compare this to a property rated D with a potential of D+ (just inside the D band). There's almost no headroom — the property is close to its ceiling without major structural work.

A small gap may indicate structural limits

If the current and potential ratings are close — say, both D — it often means the property has structural constraints the assessor can't improve around. Solid walls with no viable insulation route, for example, or a property configuration that limits what can be done.

This is useful to know before you commit to a purchase with the intention of improving it.

It affects green mortgage eligibility

Green mortgages typically require a current EPC rating of A or B. But some lenders are beginning to offer products for properties that have a potential A or B rating — effectively lending on the basis that you'll carry out the improvements. This is an emerging area and eligibility varies widely.

If you're interested in a green mortgage for a currently lower-rated property, check whether the potential score puts you in range — and what the lender requires in terms of completing the improvements.

How realistic is the potential rating?

This is where the potential score requires some scepticism. The figure is calculated by a formula, not a builder — and it has limitations.

• Listed buildings. The potential score might show C or B, but if the property is listed, many of the improvements that would get it there — external insulation, replacement windows — may require listed building consent that will be refused.
• Flats. Improvements to a flat's walls, roof, or communal heating system may require the consent of other leaseholders and the freeholder. The potential score doesn't account for this.
• Optimistic assumptions. Some assessors are more generous than others in what they recommend. If the potential improvements include solar panels on a partially shaded roof, or a heat pump in a property with no space outside, treat the potential figure with caution.
• The methodology is fixed. The potential score only includes improvements the SAP calculation recognises. New technologies — heat batteries, certain hybrid systems — may not be fully captured.

How to read the potential score properly

Rather than just noting the potential band, read the accompanying recommendations and cross-reference them against the features table:

1. Are the recommended improvements physically possible? External wall insulation on a flat in a block requires a freeholder's consent. A heat pump requires outdoor space. Check these aren't theoretical recommendations.
2. Are they permitted? Listed buildings, conservation areas, and some leasehold agreements restrict what can be done. Check planning constraints before relying on the potential rating.
3. What do they cost? The certificate gives estimated costs for each improvement. Add them up. If getting from E to C requires £20,000 of work, that's your actual upgrade cost — not a reason to dismiss the property, but a figure to factor into your offer.
4. How old is the certificate? A potential score on a 2015 EPC may already have been partly achieved. If the seller has fitted new insulation since the survey, the current rating may already be higher than the certificate shows.

Using the potential score in practice

The most useful application of the potential score is as a filter when comparing properties. Two properties both rated D are not the same if one has a potential of B and the other has a potential of D+.

The one with the B potential is a property where investment in improvements will meaningfully reduce your running costs and potentially your mortgage rate. The one with the D+ potential is close to its ceiling — further improvement is unlikely without significant structural work.

If you're choosing between similarly priced properties, the gap between current and potential is a useful — and underused — data point.