About
Why BuildPayTools exists
Construction payment arithmetic is not difficult, but it is unforgiving. A percentage taken from the wrong base, retainage applied in the wrong order, or a schedule that does not sum to the contract — each is a small mistake that becomes an argument with an owner.
What we build
Free calculators covering how contractors actually get paid: progress payments, AIA-style payment applications, retainage, draws, change orders, payment schedules, cash flow and late payment interest. Every one runs in your browser and none of them ask for an account first.
How we handle the numbers
Calculations use decimal arithmetic with explicit half-up rounding rather than floating point, so figures match a properly configured accounting system to the cent. Each formula is verified against a fixed set of test vectors before release, and the same vectors run against both the browser and the server so the two can never disagree.
Every page publishes the formulas it uses, a fully worked example, and the mistakes that most often produce a wrong application. If a figure looks wrong you should be able to trace exactly how it was reached.
What we will not do
We do not invent statistics, search volumes, reviews or ratings. We do not give legal, accounting or tax advice, and we do not tell you what you are entitled to charge — retainage rates, prompt-payment rules and what may be billed for stored materials vary by contract and jurisdiction, so the tools compute what you enter and say plainly what varies.
BuildPayTools is not affiliated with, endorsed by, or sponsored by The American Institute of Architects, and reproduces no AIA document.
Where it goes next
The calculators stay free. Paid plans add the work that happens after the calculation — saving it against a project, reusing customer details, tracking retainage across periods and producing branded documents. See pricing for what that includes.
Get in touch
Questions, corrections or a formula you think we have wrong — [email protected]. Corrections in particular are welcome; accuracy is the whole product.