How to use this calculator
- Enter or choose early start (ES).
- Enter or choose duration.
- Enter or choose late finish (LF).
- Enter or choose earliest early start of successors.
- The total float updates as you type. Use Copy result or Share to keep it.
Method
EF = ES + Duration; LS = LF − Duration; Total float = LF − EF = LS − ES; Free float = ES(successor) − EF
- ES, EF
- early start and finish from the forward pass
- LS, LF
- late start and finish from the backward pass
Worked example
- EF = 10 + 5 = 15; LS = 20 − 5 = 15.
- Total float = 20 − 15 = 5 days.
- Free float = 17 − 15 = 2 days.
The activity can slip 2 days without affecting its successor and 5 days without delaying the project.
What the result means
Activities with zero total float are on the critical path. Negative float means the schedule already misses a required date and needs recovery.
Assumptions and limits
- Finish-to-start links with no lag.
- Day numbers use the convention that an activity starting at ES finishes at ES + duration.
- Covers one activity; it does not compute the network’s forward and backward passes.
Questions
Who owns the float?
It depends on the contract. Many contracts say float belongs to the project, which affects delay claims.
Can free float exceed total float?
No. Free float is always less than or equal to total float.
Please note: Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.