In project management, getting an early indication of problems is the silver bullet that allows the project manager to correct the problems before they start.
Schedule Variance, usually abbreviated as SV, is one of the fundamental outputs of Earned Value Management. It tells the project manager how far ahead or behind the project is at the point of analysis (usually right now).
Formula
Where:
- SV = Schedule Variance
- EV = Earned Value
- PV = Planned Value
All units are monetary (dollars, euros, etc.).
Interpretation of Results
- If SV is negative, the task is behind schedule.
- If SV is zero, the task is on schedule
- If SV is positive, the task is ahead of schedule.
For example,
- SV = -$500 means the project is behind schedule.
- SV = $0 means the project is right on schedule.
- SV = $500 means the project is ahead of schedule.
Background
Schedule Variance represents the monetary value that the task is behind or ahead of schedule, relative to the task budget. For example, let’s say the task Build Fence has a budget of $4,000 and the schedule variance is $1,000. This would represent a project that is significantly ahead of schedule.
Schedule variance must be calculated on a task by task basis and summed to determine the overall project’s schedule variance.
It must have a time point of reference, in other words, it is a “snapshot” at a certain point in time. Whenever the project is active the schedule variance is changing. To put it another way, the project is getting more ahead or behind schedule as time goes on and as work goes on.
Schedule Baseline
In order to calculate the schedule variance, the project must initially be divided into tasks and each task must be assigned the following data:
- Start and Finish Dates
- Budget
This is called the schedule baseline, and it gives the project manager something to track against. Project scheduling is one of the fundamental aspects of project management.
Planned Value (PV)
Also known as Budgeted Cost of Work Scheduled (BCWS), Planned Value is the amount of the task that is supposed to have been completed, in terms of the task budget. It is calculated from the project budget.
For example, if it’s Feb. 15 today, and the task is supposed to last from Feb. 10 to Feb. 20, it should be 50% complete. If the task budget is $4,000, PV = 50% x $4,000 = $2,000.
Earned Value (EV)
Also known as Budgeted Cost of Work Performed (BCWP), Earned Value is the amount of the task that is actually completed. It is also calculated from the project budget.
For example, if the actual percent complete is 75% and the task budget is $4,000, EV = 75% x $4,000 = $3,000.
Example
Let’s say we have a project with two tasks, building a fence and laying sod. The initial schedule baseline is:
| ID | Task | Start date | End Date | Budget |
|---|---|---|---|---|
| 100 | Build Fence | Feb. 10 | Feb. 20 | $4,000 |
| 200 | Lay Sod | Feb. 12 | Feb. 25 | $3,000 |
| TOTAL | $7,000 | |||
Let’s say it’s Feb. 15. Determine the Schedule Variance for the project.
Step 1: Determine the percent complete for each task. Since this is not a real project we have to assume the tasks are 75% and 10% complete, respectively.
We will add a percent complete column to the table.
| ID | Task | Start date | End Date | Budget | % Complete |
|---|---|---|---|---|---|
| 100 | Build Fence | Feb. 10 | Feb. 20 | $4,000 | 75% |
| 200 | Lay Sod | Feb. 12 | Feb. 25 | $3,000 | 10% |
| TOTAL | $7,000 | ||||
Step 2: Determine Planned Value (PV).
Task 100 should be 50% complete, given the start and end dates of Feb. 10 and Feb. 20, respectively. Therefore PV = 50% x $4,000 = $2,000.
Task 200 should be 3 out of 13 days complete, which is 23%. Therefore, PV = 23% x $3,000 = $690.
We will add a column called PV.
| ID | Task | Start date | End Date | Budget | % Complete | PV |
|---|---|---|---|---|---|---|
| 100 | Build Fence | Feb. 10 | Feb. 20 | $4,000 | 75% | $2,000 |
| 200 | Lay Sod | Feb. 12 | Feb. 25 | $3,000 | 10% | $690 |
| TOTAL | $7,000 | $2,690 | ||||
Step 3: Determine Earned Value (EV)
Task 100 is actually 75% complete, therefore EV = 75% x $4,000 = $3,000.
Task 200 is 10% complete, therefore EV = 10% x $3,000 = $300.
Now we will add a column called EV.
| ID | Task | Start date | End Date | Budget | % Complete | PV | EV |
|---|---|---|---|---|---|---|---|
| 100 | Build Fence | Feb. 10 | Feb. 20 | $4,000 | 75% | $2,000 | $3,000 |
| 200 | Lay Sod | Feb. 12 | Feb. 25 | $3,000 | 10% | $690 | $300 |
| TOTAL | $7,000 | $2,690 | $3,300 | ||||
Step 4: Determine Schedule Variance (SV)
SV = EV – PV.
| ID | Task | Start date | End Date | Budget | % Complete | PV | EV | SV |
|---|---|---|---|---|---|---|---|---|
| 100 | Build Fence | Feb. 10 | Feb. 20 | $4,000 | 75% | $2,000 | $3,000 | $1,000 |
| 200 | Lay Sod | Feb. 12 | Feb. 25 | $3,000 | 10% | $690 | $300 | -$390 |
| TOTAL | $7,000 | $2,690 | $3,300 | $610 | ||||
The overall project schedule variance is positive $610, therefore the project is ahead of schedule. Even though the second task is behind schedule, the first task is ahead of schedule by a greater amount, therefore the project is in good shape overall.
Related Earned Value Metrics
The schedule variance is normally analyzed in conjunction with the cost variance (CV), which tells you how far over or under budget, rather than ahead or behind schedule, the project is.
- SV and CV are positive: The project is ahead of schedule and under budget (hooray!)
- SV is positive and CV is negative: The project is ahead of schedule but over budget. In other words, more tasks have been performed than were scheduled at this point, but the tasks that have been performed are over budget.
- SV is negative and CV is positive: The project is under budget but behind schedule. In other words, less tasks have been performed than were scheduled at this point, but the tasks that have been performed are under budget.
- SV and CV are negative: The project is behind schedule and over budget (boo!)
The Schedule Performance Index (SPI) is similar to SV but is relative to the task budget. It gives you an idea how far ahead or behind schedule the task is relative to the overall task budget. As you can imagine, a -$1,000 schedule variance is significant to a $7,000 fence building project but not to a billion dollar oil platform project.
