Project Timeline Calculator Formula

Understand the math behind the project timeline calculator. Each variable explained with a worked example.

Use the Project Timeline Calculator

Formulas Used

Weeks Needed

weeks_needed = ceil(buffered_hours / hours_per_week)

Months (approx)

months_needed = buffered_hours / hours_per_week / 4.33

Total Hours (with buffer)

buffered_total = buffered_hours

Variables

VariableDescriptionDefault
total_effort_hoursTotal Effort (Hours)(hrs)120
hours_per_weekHours Available Per Week(hrs/week)20
buffer_pctBuffer for Unknowns(%)20
buffered_hoursDerived value= total_effort_hours * (1 + buffer_pct / 100)calculated

How It Works

How to Estimate a Project Timeline

Divide total effort by weekly available hours, then add a buffer for unknowns and scope changes.

Formula

Buffered Hours = Effort x (1 + Buffer %)

Weeks = Buffered Hours / Hours Per Week

Worked Example

120-hour project, working 20 hours/week, with 20% buffer.

total_effort_hours = 120hours_per_week = 20buffer_pct = 20
  1. 01Buffered hours = 120 x 1.20 = 144 hours
  2. 02Weeks needed = ceil(144 / 20) = 8 weeks
  3. 03Months = 8 / 4.33 = 1.8 months

Ready to run the numbers?

Open Project Timeline Calculator