Freezing the baseline: why the GMP should be versioned, never edited

Somewhere on most owner teams there is a spreadsheet called something like Budget Tracker Final v7. It started as the GMP. Someone added a column for change orders. Someone else updated the contingency cell when a draw came in. A third person corrected an allowance amount that turned out to be wrong in the amendment. Eighteen months later, the spreadsheet is the project's memory and nobody can say what the original GMP looked like.

The problem is not the spreadsheet. The problem is that the baseline was edited instead of versioned.

What a baseline is for

A baseline is a fixed point of comparison. The GMP amendment, on the day it is signed, is the baseline for everything that follows: the contingency balance, the allowance amounts, the buyout targets, the fee basis, the schedule of values. Every later question takes the form of how far are we from that point. If the point moves, the question has no answer.

Consider a fictional $45 million research building. The amendment sets contractor contingency at $1.8 million. In month nine, a reclassification moves $120,000 from a change order back into a contingency draw, and someone updates the contingency opening balance to $1.68 million to make the spreadsheet balance. From that day forward, every burn rate calculation is wrong by $120,000, and the error is invisible because the only record of $1.8 million is in a PDF nobody opens.

Versioning instead

Versioning means the original is stored once and never touched. Every change is a new record layered on top, with a date, a reason, and a reference. Version 1 is the signed amendment. Version 2 is version 1 plus change order 1. Version 14 is version 13 plus change order 13. At any time the owner can read the current position or any earlier position, and the difference between any two versions is a list of the changes between them.

This is how accounting systems work and how contract administration has always worked on paper. The contract sum is the original sum plus executed changes. Nobody crosses out the original sum on the signed agreement. The spreadsheet habit of editing in place arrived because spreadsheets make it easy, not because it was ever a good idea.

What gets versioned

The GMP total, obviously. But also each line of the estimate, each allowance amount, the contingency opening balance, the fee basis, the general conditions basis, the qualifications list, and the drawing list. A change order may touch several of these at once. Each touched item gets a new version tied to that change order, and the old version stays readable.

Corrections are versions too

The hardest case is a mistake in the baseline itself. The amendment says an allowance is $300,000 but the estimate behind it clearly shows $350,000, and everyone agrees it was a typo. The temptation is to fix the number. The better path is to record a correction as its own version, dated, with the reason and the evidence attached. The baseline still says $300,000. Version 2 says $350,000 with a note that says why.

Under most AIA A133 based agreements, a correction to the GMP is itself a change order, even if no money moves. Check your contract. Either way, the owner's record should show the correction as an event rather than a silent edit.

Why this matters at closeout and in a dispute

At closeout, the savings calculation starts from the adjusted GMP, which is the baseline plus all executed change orders. If the baseline has been edited, the adjusted GMP cannot be reconstructed and the savings figure rests on whatever the spreadsheet currently says. In a dispute, the first thing each side will try to establish is what the contract said on the day it was signed. An owner whose baseline is a living spreadsheet has no way to prove it.

Costwitness freezes the GMP amendment as version one and records every change order, reclassification and correction as a numbered version on top, so the original and the current position can both be read and the path between them can be traced. The rule is enforced by the software. The reason for each version still has to be written by a person.

In the product

GMP baseline, Change order register, Anticipated final cost. Free tool: Pre-GMP Readiness Score, Change Order Exposure.

Keep reading

Earlier: AIA A133 and A102: the GMP clauses owners should know by heart. Later: Owner audit rights under a GMP contract, and how to use them. All articles on gmp contracts.