Free calculator
Total float and free float calculator
Enter an activity's dates or working-day numbers, its late finish, and the early start of its first successor. Total float and free float update as you type.
Day numbers count working days from the project start, with the finish at the end of the last day: an activity starting on day 10 with a 5-day duration finishes on day 15. The example figures are hypothetical.
Early finish
–
Late start
–
Total float
–
Free float
–
Float formulas
| Measure | Formula | What it tells you |
|---|---|---|
| Early finish (EF) | EF = ES + duration | The earliest the activity can finish, from the forward pass. |
| Late start (LS) | LS = LF − duration | The latest it can start without delaying the finish, from the backward pass. |
| Total float (TF) | TF = LS − ES = LF − EF | How far it can slip before the project finish moves. Zero or less is critical. |
| Free float (FF) | FF = min(ES of successors) − EF | How far it can slip before any successor moves. Assumes finish-to-start links with no lag. |
A worked example
Suppose a hypothetical slab pour lasts 5 working days, can start on day 10 at the earliest, and must finish by day 22 for the project to finish on time. Its successor, the formwork strip, can start on day 18 at the earliest.
- Early finish is 10 + 5 = day 15, and late start is 22 − 5 = day 17.
- Total float is 17 − 10 = 7 working days. The pour can slip about a week and a half before the project finish moves.
- Free float is 18 − 15 = 3 days. After 3 days of slip, the formwork strip starts to move too.
Float on a real programme
On a full programme the scheduling tool does this for every activity at once, across calendars, lags and constraints. The free schedule viewer opens a P6, MS Project or Powerproject file in the browser and shows each activity's total float and critical flag as your scheduling tool recorded them, with the critical path highlighted. For what float means in a delay claim, see total float vs free float.
Questions
- What is the total float formula?
- Total float = late start − early start, which is the same as late finish − early finish. It is how far the activity can slip before it delays the project finish.
- What is the free float formula?
- Free float = the earliest early start of the activity's successors − the activity's early finish, for finish-to-start links with no lag. It is how far the activity can slip before it delays any successor.
- How do you calculate float from dates?
- Count working days only. Total float is the number of working days after the early finish date, up to and including the late finish date. Free float is the number of working days after the early finish date and before the successor's early start date. An activity finishing on a Friday whose successor can start on the Monday has no free float on a Monday-to-Friday week.
- Can free float be larger than total float?
- Not while total float is zero or more: delaying a successor is the first thing that can happen as an activity slips. When a constraint drives total float negative, free float can still be zero or positive, because it is measured against the successors, not the constraint.
- What does negative total float mean?
- The activity's late finish is earlier than its early finish, so the programme cannot meet a date it is required to meet. On a real programme that is usually a constraint on a milestone, such as a contract completion date, that the logic cannot reach.
- Why does my scheduling tool show different float from this calculator?
- P6, MS Project and Powerproject work in calendar dates and working hours, apply each activity's calendar and constraints, and may calculate float on start dates, finish dates or the smaller of the two. This calculator uses whole working days on one fixed working week, with no public holidays, activity calendars or constraints, so it explains the arithmetic rather than reproducing a tool's figure.