Where the money is decided, and where it is spent.
This page has no calculator on it, because there is nothing honest to calculate. It is a pattern the industry recognizes, drawn without a single measured value on either axis.
Cost Influence Curve
Two lines that cross. Early on you can change almost anything for almost nothing. Late on you can change almost nothing without paying for it twice.
No axis on this chart carries a measured value, and that is deliberate. The shape is a pattern the construction industry recognizes, not a figure Costwitness has measured. Anyone who puts numbers on these axes is selling you something.
Why the GMP moment matters
A guaranteed maximum price is normally signed somewhere between design development and construction documents. That is the point where the two lines are closest: you still have some ability to influence the cost, and a change does not yet cost a fortune. Every week after it, the trade worsens.
What follows from it
It is why the readiness of the drawings at that moment predicts the argument you will have eighteen months later, and why a contingency set against incomplete drawings is not a number, it is a bet. Both of those have calculators of their own.
One pay application, six checks.
Send me one pay application and I will run six checks against the schedule of values it came from. Free, one G703, names redacted, written answer in two working days.