UK New Build Mortgage Calculator
Calculate your mortgage for a new build property in the UK. Covers lender minimum deposit rules (10% houses, 15% flats), Deposit Unlock scheme, down-valuation risks, builder incentives, and NHBC warranty value.
New build mortgages have stricter lending criteria than existing properties. Most mainstream lenders apply these rules.
New builds typically sell at a 10–15% premium over equivalent existing properties. This premium tends to decay in the first 5 years as the property becomes "second-hand."
How to Use This New Build Mortgage Calculator
Enter the new build price, your deposit, mortgage rate, and term. Select whether you are buying a house or flat — this determines the minimum deposit your lender will require. The calculator shows your monthly payment, total interest, and stamp duty, plus flags if your deposit falls below lender minimums.
New build mortgages have stricter criteria than standard mortgages. This calculator is designed specifically for new build buyers to understand the rules before applying.
New Build Deposit Requirements
New build flat: 15% minimum deposit (most lenders)
High-rise flat: Often 25%+ (above 6 storeys)
Existing property: 5% minimum (for comparison)
Deposit Unlock scheme: 5% for new build houses
(volume builders + participating lenders only)
The higher deposit requirement for new builds exists because lenders consider the new build premium and the risk that the property may be valued below the purchase price by their independent surveyor.
Example: Buying a New Build House
Tom and Emma — £380,000 New Build House in Milton Keynes
| Purchase Price | £380,000 |
| Deposit (10%) | £38,000 |
| Mortgage | £342,000 |
| Rate (2-year fixed) | 4.75% |
| Monthly Payment (25yr) | £1,935 |
| Stamp Duty (standard buyer) | £6,500 |
| Builder offered: stamp duty paid | -£6,500 |
| Effective price after incentive | £373,500 |
| NHBC 10-year warranty | Included |
Tom and Emma benefit from the builder paying their stamp duty — a £6,500 saving. However, they must disclose this to their lender as it is a financial incentive.