When building your schedule, never guess times. Gather the most reliable information possible and use a scientific formula to get the best estimate. The better your estimates, the more reliable your plan will be.

This formula is considered the standard for estimating time (Te):



  • Tm= Probable Time
  • To= Optimistic Time
  • Tp=Pessimistic Time
  • Te=Calculated Time (Best Estimate)

First, make a table, list your tasks, and fill in the estimated time for each. (We have numbered our tasks in the example on the next page for easy identification.) Time can be listed in minutes, hours, days, weeks, months, or years. You should keep the same time scale for each task.

Next, identify what the best and worst case estimates would be. Now, for each task, plug the numbers into the formula given above. The result is the estimated time.


Probable Time

Optimistic Time

Pessimistic Time

Calculated Time

  1. Get paint samples
  1. Choose a paint color
  1. Remove all furniture
  1. Take off trim
  1. Paint trim
  1. Apply first coat
  1. Apply second coat
  1. Put trim back in
  1. Put all furniture back in