Self-Build Mortgage Calculator
Budget a UK self-build: total project cost, stage-released loan, and the equity you'll create.
Self-build reality — 15–20% is standard.
Market value of the finished property.
Self-build lenders often want 25%+.
Typically 1–2% above standard residential.
A UK self-build with total costs of £0 and an end value of £0 creates £0 in equity, needing a £0 mortgage drawn in stages.
How a self-build mortgage works
Stage releases
Most UK self-build lenders release funds in 5–6 stages: purchase/foundations, wall plate, watertight, plastered, second fix, final. Arrears-basis lenders release after inspection; advance lenders release upfront for each stage.
Contingency is critical
15–20% contingency is standard. Groundworks, weather delays, material price rises and scope creep routinely push UK self-builds over budget. Lenders often require proof of contingency funds before approving.
Frequently asked questions
How does a self-build mortgage work?
The loan is released in stages as the build progresses (foundations, wall plate, watertight, plastering, completion). Most lenders release on an 'arrears' basis — you fund each stage, then claim. A handful offer 'advance' stage releases which fund upfront.
What deposit do I need?
UK self-build lenders typically want 25%+ of total project cost (land + build + contingency). A few accept 20%. Owning the land already with no mortgage effectively contributes to the deposit.
Are self-build rates higher?
Yes, typically 1–2% above standard residential during the build, reflecting higher lender risk. After completion, most borrowers remortgage onto a standard residential product at better rates.
Can I reclaim VAT on a self-build?
Yes — HMRC refunds VAT on most new-build materials and some services. Submit a DIY Housebuilders' VAT reclaim within 3 months of completion. Extensions and conversions have different rules.
How much contingency should I budget?
15–20% of build cost is standard. UK self-builds regularly run 5–15% over budget on materials, labour and unforeseen groundworks. Lenders often require evidence of contingency funds before approving.
Reviewed by the Mortgage118 editorial team. Build-year interest is an estimate assuming 50% of the loan drawn on average over 12 months. Individual stage-release schedules vary. Provides an estimate only.