Schedule Performance Index (SPI)
The Schedule Performance Index, or SPI, tells you how efficiently your project is progressing against its planned timeline. It uses two terms. "Earned Value" (EV) is the budgeted value of the work you have actually completed so far. "Planned Value" (PV) is the budgeted value of the work you were supposed to have completed by this same point in time, according to your schedule. SPI is EV divided by PV.
Here's how to read it. SPI compares how much work is truly done versus how much should be done by now. An SPI above 1 means you've completed more than planned — you're ahead of schedule. An SPI below 1 means you've completed less than planned — you're behind schedule. An SPI of exactly 1 means you're right on time.
A project manager uses SPI to answer "Are we on track with time?" One important note: SPI measures schedule in terms of the value of work done, not calendar dates, so it's a helpful early warning that pace is slipping. As a project nears its end, though, SPI naturally drifts toward 1, so managers rely on it most in the early and middle stages.
Think of it like a road trip where your map says you should be 100 km along by lunchtime, but you've only covered 90 km. Dividing what you've actually traveled by what you planned to travel tells you whether you're keeping pace, running ahead, or falling behind.
Imagine that by today, your schedule said you should have finished ₹1,00,000 worth of work — that's your Planned Value (PV = ₹1,00,000). In reality, the work you've completed adds up to a budgeted value of ₹90,000 — that's your Earned Value (EV = ₹90,000). SPI = EV ÷ PV = 90,000 ÷ 1,00,000 = 0.9. An SPI of 0.9 means you've done only 90% of the work you planned to by now, so you're slightly behind schedule.
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