Project Time Calculator

Schedule Variance and SPI Calculator: Forecast the Time to Complete

Enter planned value and earned value to get the schedule performance index, the schedule variance and a forecast of how long the project will take.

Quick answer

Schedule performance index (SPI) = earned value ÷ planned value. Schedule variance = EV − PV. With EV 40,000 and PV 50,000, SPI is 0.8 and the schedule variance is −10,000. At that pace a 20-week plan takes 20 ÷ 0.8 = 25 weeks, so the delay is 5 weeks.

Value of work planned by now.
Value of work actually done.
Total planned time for the project.
Adds cost variance and CPI.
Adds percent complete and EAC.

How to read your result

Enter planned value (PV): the value of the work you planned to have finished by now. Enter earned value (EV): the value of the work actually finished. Add the planned total duration to get a forecast. Actual cost (AC) and budget at completion (BAC) are optional and unlock the cost side.

  • SPI: EV ÷ PV. Below 1 means behind schedule, 1 on schedule, above 1 ahead. 0.8 means 80% of the planned progress has been achieved.
  • Schedule variance (SV): EV − PV, in the same units as PV and EV. Negative is behind.
  • Forecast duration: planned duration ÷ SPI, assuming the schedule efficiency to date continues. Expected delay is the forecast minus the plan.
  • CV, CPI, EAC, percent complete appear when you add AC and BAC: cost variance EV − AC, cost index EV ÷ AC, estimate at completion BAC ÷ CPI, and EV ÷ BAC.

The tool also names the band your SPI falls in. The SPI meaning guide explains every band from 0.5 to 1.5 with the delay each implies.

Schedule variance and SPI formulas

SV = EV − PV    SPI = EV ÷ PV

forecast duration = planned duration ÷ SPI    delay = forecast − planned

CV = EV − AC    CPI = EV ÷ AC    EAC = BAC ÷ CPI    percent complete = EV ÷ BAC

These are the standard earned value management formulas. The duration forecast is a simple extrapolation: it assumes the rest of the project runs at the same schedule efficiency as the work so far. PV, EV and AC must use the same currency or unit, and PV and EV must refer to the same date.

Worked examples

Each example uses numbers you can load into the calculator above; the results match the tool exactly.

Example 1 (simple): PV 50,000, EV 40,000, 20 weeks planned

  • SPI = 40,000 ÷ 50,000 = 0.8 (behind: 80% of planned progress)
  • SV = 40,000 − 50,000 = −10,000
  • Forecast = 20 ÷ 0.8 = 25 weeks; delay = 5 weeks late

These are the calculator's default inputs.

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Example 2: ahead of plan, PV 120, EV 132, 30 weeks planned

  • SPI = 132 ÷ 120 = 1.1 (ahead)
  • Forecast = 30 ÷ 1.1 = 27.27 weeks; delay = 2.73 weeks early

An SPI above 1 is good news only if the plan was realistic; check that quality has not slipped.

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Example 3 (realistic): schedule and cost together

PV 60,000, EV 54,000, AC 63,000, BAC 200,000 and a 40-week plan.

  • SPI = 54,000 ÷ 60,000 = 0.9; forecast = 40 ÷ 0.9 = 44.44 weeks (4.44 weeks late)
  • CV = 54,000 − 63,000 = −9,000; CPI = 54,000 ÷ 63,000 = 0.86
  • EAC = 200,000 ÷ 0.857 = 233,333; percent complete = 54,000 ÷ 200,000 = 27%

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Using SPI to calculate the time to complete a project

The forecast duration is the planned duration divided by SPI. It answers "if the rest of the project keeps going at the rate the work so far has gone, how long does the whole thing take?" Subtract the time already elapsed to get the time remaining. For a 20-week plan with an SPI of 0.8, the whole project takes 25 weeks; if 10 weeks are already gone, 15 remain.

Two cautions apply. SPI measured by value is not the same as being late on the critical path: a project can have a healthy SPI while the critical path slips, so check the critical path as well. And SPI converges to 1 as a project finishes, because EV catches up with PV, so late-project SPI says little about delay. For a simple estimate from progress and elapsed time, use the estimated time remaining calculator.

How to calculate SPI and the forecast by hand

  1. Find PV: the value of work planned to be done by the status date.
  2. Find EV: the planned value of the work actually completed.
  3. Divide. SPI = EV ÷ PV = 40,000 ÷ 50,000 = 0.8.
  4. Subtract for the variance. SV = EV − PV = −10,000.
  5. Forecast. Planned duration ÷ SPI = 20 ÷ 0.8 = 25 weeks; the delay is 25 − 20 = 5.

Assumptions, limits and common mistakes

Assumptions and limits

  • The forecast assumes today's schedule efficiency continues. If the cause of the delay is fixed, the real delay will be smaller.
  • PV and EV must be measured on the same date and in the same unit, and EV must use the baseline planned value of finished work, not what it cost.
  • SPI is a value-based measure. It does not say which tasks are late or whether the critical path is affected.
  • Cost forecasts (EAC) use the simple BAC ÷ CPI formula; other EAC methods exist.

Common mistakes

  • Using actual cost as earned value. EV is the planned value of what is done; actual cost is AC.
  • Comparing PV for one date with EV for another. They must be at the same status date.
  • Reading SPI near the end of a project. It tends to 1 as work completes, whatever the real delay.
  • Treating the forecast as a promise. It is a trend, not a commitment.

Frequently asked questions

What is SPI in project management?

The schedule performance index is earned value divided by planned value. Below 1 means behind schedule, 1 on schedule and above 1 ahead.

How do I calculate schedule variance?

Subtract planned value from earned value: SV = EV − PV. A negative number means you are behind. With EV 40,000 and PV 50,000 the variance is −10,000.

How do I use SPI to estimate time to complete a project?

Divide the planned duration by SPI. A 20-week plan with an SPI of 0.8 forecasts 25 weeks, a delay of 5 weeks. Subtract the time already elapsed for the time remaining.

What is a good SPI?

1.0 or above means on or ahead of plan. Between 0.9 and 1.0 is a small slip many teams treat as normal; below 0.8 usually needs action. See the SPI bands.

What is the difference between SPI and CPI?

SPI compares earned value with planned value (schedule). CPI compares earned value with actual cost (cost). Both use EV as the numerator.

Can SPI be above 1 while the project is late?

Yes. SPI uses value, so completing easy, low-value work first can lift it while critical-path tasks slip. Check the critical path as well.

Where do I get PV and EV?

PV comes from your baseline schedule and budget; EV is the baseline value of the tasks completed. Many project tools report both. Use the same status date for both.

Last updated 19 October 2026. Last reviewed 19 October 2026. Reviewed by . Formulas and tests: methodology.