How to read an S-curve on a construction loan draw
If you've sat through more than a few draw meetings, you've seen the chart: a soft curve that starts flat, climbs steep through the middle of the job, then flattens out again near closeout. That's the S-curve, and it's usually the first thing a lender's construction risk group flips to in the draw package. Here's what it's telling you, and what it isn't.
What the two lines on the curve are
A cumulative cost curve plots money spent (or earned, depending on how the GC built it) against time, running from zero at notice to proceed up to 100% at substantial completion. Plot it against the schedule and you get the classic S shape: slow early because mobilization, permitting, and site work don't burn much budget fast; steep in the middle when structure, enclosure, and MEP rough-in are all running at once; slow again at the end because punch list and closeout items cost little relative to the labor they take.
Most draw packages show two versions of that line. The planned curve comes from the baseline schedule and budget, set before the first shovel. The actual curve is built from what's been billed, usually tied to the schedule-of-values line items the GC submits with the application for payment. When people talk about "planned vs actual," this is the comparison: the curve the job was supposed to follow against the curve it's tracing on site.
Reading the gap
The whole point of putting both lines on one chart is the space between them. If actual sits above planned, the contractor has billed more than the schedule called for at this point. That's not automatically good. It can mean the job is ahead of schedule, or it can mean the schedule-of-values was front-loaded so early requisitions draw more than the work in place justifies. If actual sits below planned, the job may be behind, or it may just mean a draw got held up in review and the percentage hasn't caught up on paper yet.
The gap tells you direction and rough magnitude. It doesn't tell you why. That's the limit worth understanding before you sign off on an application for payment: the cumulative cost curve is built from a self-reported schedule of values, not from anyone walking the site and counting units in place. A GC can be entirely honest and still be reporting percent-complete the way the contract defines it, cost incurred against cost budgeted, which isn't the same question as how much is physically built.
Where it gets misleading
This is the part that trips up a lot of draw reviews. A foundation pour and a finish-carpentry package can represent the same dollar value on a schedule of values and look identical on the cost curve, but one of them you can verify by standing on site for five minutes and the other takes a walkthrough with a punch list. The curve smooths all of that into one percentage. So does the self-reported number on the AIA G702/G703 form the draw request rides in on.
That's the gap a weekly, site-wide record is built to close. Instead of taking the contractor's claimed percent-complete as the only input, a project like Construction Progress layers a drone pass against the same schedule the S-curve is tracking, so the owner or lender has an observed percentage to put next to the requisitioned one before the draw goes out. When the two agree, the draw moves faster. When they don't, you find out before the funds do.
None of this replaces the schedule-of-values review or the architect's certification. It just gives the S-curve a second data point that didn't come from the party asking to be paid.
If you're reviewing draws on a job where the curve and the site don't seem to agree, it might be worth putting a weekly observed record next to the requisition before you sign the next one.