Schedule Variance

Schedule Variance (SV) is an Earned Value Management metric that measures the difference between the Earned Value (EV) of work actually completed and the Planned Value (PV) of work that was scheduled to be completed by a given date, expressed in cost terms.

What is Schedule Variance?

In the EVM framework, Schedule Variance is calculated as SV = EV minus PV. A positive SV means more work has been accomplished than was planned (ahead of schedule); a negative SV means less work has been completed than planned (behind schedule). The formula expresses schedule status in dollar terms, not calendar days, because it measures the budget value of schedule deviation rather than elapsed time.

For example, if the planned value at month 6 is $5M but the contractor has only accomplished $4M worth of work (earned value), the schedule variance is -$1M, meaning the program is $1M behind on accomplishing planned work. This does not directly translate to a specific number of calendar days, but a -$1M SV in a program burning $500K per month suggests approximately two months of schedule delay.

The Schedule Performance Index (SPI = EV/PV) is the ratio equivalent of schedule variance. An SPI of 1.0 means on schedule; below 1.0 means behind; above 1.0 means ahead. SV and SPI together with Cost Variance (CV) and Cost Performance Index (CPI) form the four primary EVM performance indicators.

Important limitation: as a program approaches completion, the planned value converges to the budget at completion, and the SPI tends toward 1.0 regardless of actual schedule performance. For this reason, many programs supplement SPI-based schedule analysis with an independent schedule risk assessment using the Integrated Master Schedule.

Why schedule variance matters for government contractors

Negative schedule variance on a government contract triggers reporting requirements, government inquiries, and often contract administration actions. Early detection of negative SV trends allows program managers to accelerate key activities, add resources, or negotiate scope adjustments before a modest delay becomes a contract-threatening overrun.

Example

A Navy systems contractor's monthly EVM report shows a cumulative schedule variance of -$2.4M at program month 10. The Budget at Completion is $30M, making the SV represent 8% of total program value. The Schedule Performance Index is 0.86. The program manager identifies two work packages on the critical path, antenna assembly and integration testing, as the primary drivers. Additional test technicians are assigned, and overtime is authorized on the antenna assembly line, reducing the SV to -$1.2M by month 12.

Frequently Asked Questions

Can schedule variance be measured in calendar days instead of dollars?

EVM's SV is inherently a cost-based metric measured in dollars. To convert to time, analysts can use the Schedule Performance Index to estimate time efficiency and compare against the IMS critical path for a calendar-based schedule delay estimate. Some organizations also use Earned Schedule (ES) analysis, a complementary technique that does express schedule status in time units.

Is a positive schedule variance always a good sign?

Not necessarily. A high positive SV might indicate that easy work packages were completed early while difficult ones were deferred, creating an optimistic SV that will reverse as the program progresses into harder work. Program managers should verify whether positive SV reflects genuine schedule performance or selective sequencing.

What is the relationship between SV and float in the IMS?

Schedule Variance and float are complementary but different. SV is an aggregate cost-based measure of schedule performance across all work. Float is a schedule-based measure for individual activities in the IMS. A program can show a slightly negative SV while still having adequate schedule float, or can have zero float on the critical path despite a positive overall SV if the ahead-of-schedule work is non-critical.

How does schedule variance affect contract fee?

On cost-plus-incentive-fee (CPIF) contracts with schedule incentives, significant negative schedule variance can reduce the contractor's earned fee. On other contract types, schedule variance does not directly reduce fee but may affect past performance ratings and the government's confidence in the contractor's ability to complete on time.