Costing calculators
10 costing calculators: cost per square metre, concrete and rebar cost, labour, formwork and scaffold cost, VAT, unit rate build-up, progress payments and variations.
What this group solves
Costing turns a quantity into money: multiply by rate, add preliminaries, apply overheads and tax. A unit rate is labour plus material plus plant plus management plus profit plus risk allowance, and each component has its own basis — apply the wrong basis and the whole rate drifts by more than 10%.
The other tools are about cash flow. VAT at the general rate or the simplified rate behaves very differently once input credit is considered; progress payments are made at the contract percentage but held back for retention (typically 3%) and recovered for mobilisation advance; variations are priced against an existing similar rate before a new rate is built up. These are the items that turn into disputes at final account, so price them before you negotiate.
The arithmetic here is simple; the errors are all about convention — tax-inclusive or not, preliminaries included or not, what base progress payments deduct retention and advance from. The same job can differ by more than 20% depending on which convention is used. Establish 'who is this number for' first: a tender, a cost check and a payment application all use different conventions.
Which one for your case
| Quick cost per square metre | Cost per Square Metre Estimator |
| Elemental cost for concrete, rebar, formwork or scaffold | Concrete Cost Calculator |
| Converting between tax-inclusive and tax-exclusive prices | Construction VAT Calculator |
| Building a composite unit rate | Unit Rate Build-up Calculator |
| How much to claim this period | Progress Payment Calculator |
| Pricing a variation order | Variation Order Cost Calculator |
Where this group goes wrong
- Multiplying a tax-exclusive rate by a tax-inclusive quantity, or the reverse. Construction services are 9% under general VAT and 3% under simplified VAT, and the two cannot be mixed — on a 10 million contract one mix-up is 600,000.
- Leaving preliminaries out of the composite rate. A billed composite rate covers labour, material, plant, overhead and profit only; scaffolding and formwork sit in the preliminaries bill, so adding them twice or omitting them twice are both wrong.
- Computing a progress payment as contract sum × percentage complete, forgetting the advance recovery and retention. Advances of 10-30% are recovered pro rata and retention is 3%, so cash received runs 15-25% below the arithmetic.
- Claiming only direct cost on a variation. A change drags preliminaries, time and overhead with it; claiming direct cost alone means financing that for the client.