Use this calculator to see how much the Warm Homes Loan Scheme could cut the cost of borrowing for a heat pump, solar panels or a battery. Enter the loan amount, the rate the lender would normally charge and the term. It shows the lowest rate the government grant allows, your monthly payment and how much interest you would save.
Built on the grant method in the Warm Homes Loan Scheme rules (version 3, September 2026). Last checked on 28 October 2026.
Warm Homes Loan calculator
Enter a lender's normal rate to see the lowest rate the government grant allows.
£500 to £100,000
Fixed rate, 0% to 25%
1 to 30 years
Rate with the government grant
3%instead of 8%
| Measure | Normal rate | With the grant |
|---|---|---|
| Monthly payment | £155.86 | £132.13 |
| Total interest | £3,092 | £1,099 |
| You save | £1,993 over 84 months | |
Shows the largest cut the scheme rules allow: up to 5 percentage points, never below 0%, with the grant capped at 20% of the loan and no grant under 3 years. Lenders set their own rates and some add extra discounts, so a real quote may differ. This is an estimate, not financial advice.
Lenders may ask for an Energy Performance Certificate. Check your EPC
How the calculator works
The government pays the lender a non-repayable grant once your installation is verified, and the lender passes it on to you as a lower fixed interest rate. The scheme rules set four limits:
- The rate can be cut by up to 5 percentage points below the lender's normal rate.
- The rate can never go below 0%.
- The grant is capped at 20% of the loan.
- Loans shorter than 3 years get no grant.
The calculator follows the rules' own four-step method:
- Work out the monthly payment at the lower target rate.
- Work out how much of the loan that payment would repay at the lender's normal rate.
- The difference is the grant.
- Cap it at 20% of the loan.
It then picks the lowest target rate that stays within all four limits.
We tested it against the rules' published table of grant percentages and the government's own example. A £10,000 loan over seven years at 8% costs about £156 a month. Through the scheme at 3%, it costs about £132 a month.
What the numbers show
Best scheme rate on a £10,000 loan, by the lender's normal rate and the term:
| Lender's normal rate | 5 years | 10 years | 20 years |
|---|---|---|---|
| 6% | 1.0% | 1.3% | 3.4% |
| 8% | 3.0% | 3.1% | 5.2% |
| 10% | 5.0% | 5.0% | 7.0% |
| 12% | 7.0% | 7.0% | 8.7% |
- Up to about 10 years, most loans get the full or nearly the full 5-point cut.
- On 20-year loans, the 20% cap limits the cut to roughly 3 points.
- The lower the normal rate, the sooner the cap bites. That is why 6% over 10 years gets a 4.7-point cut while 10% gets the full 5.
Longer terms still mean lower monthly payments, but much more interest overall. Choose the shortest term you can comfortably afford.
Before you borrow
- Compare the APR and the total amount repayable, not just the headline rate. APR includes fees.
- Get a cash quote too. A 0% deal is only good value if the installer's price is fair.
- Take the heat pump grant first. In England and Wales the Boiler Upgrade Scheme takes £7,500 off an air or ground source heat pump, so you borrow less.
- Check the deadline. Installing a heat pump, solar panels or a battery is VAT-free until 31 March 2027. From 1 April 2027 VAT returns to 5%, which raises the amount you would need to borrow.
Our Warm Homes Loan Scheme guide covers who can borrow, the loan limits for each technology, the 10 approved lenders and the catches.
Step 1 of 3
Check your EPC before you apply
Enter your postcode to see this property's current rating, expiry date and recommended improvements. Lenders may ask for an EPC, and the recommendations show whether insulation should come first.
Link to this calculator
Installers, lenders, advisers and journalists are welcome to link to this calculator. It is free to use and does not collect the numbers you enter.
Sources
- Department for Energy Security and Net Zero: Warm Homes Loan Scheme rules, version 3 (September 2026), section 6 and Appendix 6
- GOV.UK: Warm Homes Loan Scheme guide (published 28 October 2026)
- Department for Energy Security and Net Zero: Warm Homes Loan Scheme factsheet (27 October 2026)