How it works
Add the six quoted amounts, rounded individually to pence. An optional allowance is a percentage of that subtotal, not a prediction or confidence interval. Enter 0 only when a cost is genuinely zero or included elsewhere. Check VAT and delivery assumptions in each quote.
Worked example
Illustration: £1,000 building + £775 base + £200 assembly = £1,975. A chosen 10% allowance adds £197.50, giving £2,172.50. These are demonstration figures, not current prices.