UK Help to Build Calculator
Calculate your Help to Build equity loan amount (5-20% of project cost), reduced mortgage size, and monthly payments for self-build and custom-build homes in England. Includes 5-year interest-free period, year 6+ interest charges, comparison to standard self-build mortgages, and future repayment modelling based on property appreciation.
Help to Build is a government scheme that makes custom and self-build housing more affordable by providing an equity loan of 5-20% of the total project cost.
| Stage | What Happens | Amount / Detail |
|---|---|---|
| 1. Apply | Apply via an approved lender (e.g. Buildstore, Bath BS) | Free to apply |
| 2. Land & Builder | Purchase land and appoint Homes England registered builder | Land: £100,000 |
| 3. Equity Loan | Government issues equity loan agreement before build starts | £76,000 |
| 4. Drawdown | Loan drawn down in stages as build progresses | Interest-free during build |
| 5. Completion | Move in; mortgage starts; equity loan interest-free for 5 years | From month 1 |
| 6. Year 6+ | Interest charged on equity loan at RPI+1% per year | ~£285/month |
| 7. Repay Loan | Repay as % of property value when you sell or refinance | 20% of value at time of repayment |
The equity loan works like Help to Buy — you repay a percentage of the property value, not the original loan amount. This means your repayment depends entirely on what your home is worth when you repay.
| Year | Projected Property Value | Equity Loan Repayment (20%) | Interest Charge (if not repaid) | Cumulative Interest |
|---|---|---|---|---|
| Year 1 ★ | £393,300 | £78,660 | £0 (interest-free) | £0 |
| Year 2 ★ | £407,065 | £81,413 | £0 (interest-free) | £0 |
| Year 3 ★ | £421,313 | £84,263 | £0 (interest-free) | £0 |
| Year 4 ★ | £436,059 | £87,212 | £0 (interest-free) | £0 |
| Year 5 ★ | £451,321 | £90,264 | £0 (interest-free) | £0 |
| Year 6 | £467,117 | £93,423 | £3,420 | £3,420 |
| Year 7 | £483,466 | £96,693 | £3,420 | £6,840 |
| Year 8 | £500,387 | £100,077 | £3,420 | £10,260 |
| Year 10 | £536,028 | £107,206 | £3,420 | £17,100 |
| Year 15 | £636,633 | £127,327 | £3,420 | £34,200 |
| Year 20 | £756,120 | £151,224 | £3,420 | £51,300 |
How to Use This Help to Build Calculator
Enter your build cost (construction, materials, contractor fees), land cost (plot purchase price), and your deposit (minimum 5% of total project cost). Select the equity loan percentage (5-20%) and your expected mortgage rate. The calculator shows how much the government lends you, your reduced mortgage size, and monthly payment.
What Help to Build Provides
- An equity loan of 5-20% of the total project cost (land + build), up to £600,000 total
- Loan is interest-free for the first 5 years after completion
- Reduces your mortgage size, lowering monthly payments
- Loan is repaid as a percentage of your property value when you sell or refinance
- Replaces Help to Buy for self-build and custom-build homes in England
Help to Build Formula
Maximum Equity Loan = Total Project Cost × Equity Loan % (5-20%)
Mortgage Required = Total Project Cost - Equity Loan - Your Deposit
Interest after Year 5 = Equity Loan × (RPI + 1%) per year
Repayment at Sale = Current Property Value × Equity Loan %
Example: Build £280,000 + Land £100,000 = £380,000 total
20% equity loan = £76,000 from government
5% deposit = £19,000
Mortgage = £380,000 - £76,000 - £19,000 = £285,000
The critical distinction from a standard loan: you repay a percentage of the property value at repayment, not the original loan amount. If your home is worth more, you repay more.
Example: Help to Build Calculation
Sarah building a 4-bedroom house in Yorkshire
Sarah has found a plot for £90,000 and has detailed quotes from a Homes England registered builder for £270,000. She has £18,000 saved as a deposit.
| Land Cost | £90,000 |
| Build Cost | £270,000 |
| Total Project Cost | £360,000 |
| Her Deposit (5%) | £18,000 |
| Help to Build Equity Loan (20%) | £72,000 |
| Mortgage Required | £270,000 |
| Monthly Mortgage (4.9%, 25yr) | £1,562/month |
| Interest-Free Period | 5 years from completion |
| Year 6 Monthly Fee (approx.) | £324/month on equity loan |
Without Help to Build, Sarah would need a £342,000 mortgage at £1,978/month — a saving of £416/month in the first 5 years.