Learn & Understand

The Flaw in Schedule Variance: Why It Always Ends at Zero

The schedule variance calculator subtracts planned value from earned value and reports the gap in dollars, negative means behind, positive means ahead. It is a workhorse of earned value management. But it hides a genuinely strange defect that catches many practitioners off guard: no matter how catastrophically late a project runs, its schedule variance is guaranteed to arrive at exactly zero on the day it finishes. A metric that reads "perfectly on schedule" for a project delivered a year late is telling you something is wrong with the metric.

The Built-In Convergence

The oddity comes straight from the definitions. Earned value is the budgeted value of work completed; planned value is the budgeted value of work scheduled. When the project is finally, fully complete, all the work is done, so earned value equals the total budget. And once every scheduled task has been reached, planned value also equals the total budget. Two equal numbers subtract to zero. Schedule variance therefore collapses to zero at completion, by construction, regardless of how late that completion was.

Why a Late Project Reads "On Time"

This means schedule variance is least trustworthy exactly when you might most want it: at the end. A project that blew its deadline shows a shrinking schedule variance in its final stretch and a reassuring zero at the finish, because the measure is tracking work done versus work planned in dollars, not time elapsed versus time planned. It runs out of "behind" to report once all the work exists, even if the calendar tells a very different story.

The Deeper Problem: Dollars for a Time Question

The root issue is that schedule variance answers a question about time using the currency of money. Its designers accepted this so that schedule performance could sit in the same dollar framework as cost performance and be combined with it. That elegance comes at the price of the strange end-of-project behavior: a schedule measure denominated in dollars cannot help but zero out when the money-value of work planned and done finally coincide.

The Fix: Earned Schedule

Practitioners eventually devised a remedy called earned schedule, which restates the same idea in units of time rather than money, asking "at what point in the plan should we have earned what we've actually earned?" Measured that way, a late project stays visibly late right through to the end. Knowing schedule variance's zero-at-completion quirk is what tells you when to stop trusting the dollar figure and reach for the time-based view instead.

For the ratio form of schedule performance, see the Schedule Performance Index Calculator; for the full four-number framework, the Earned Value Calculator.