Purpose and scope
What this timeline establishes
Calculate successor timing from dependency relationship, duration, lead, or lag.
The Dependency Lead/Lag Calculator models checkpoints from Predecessor starts, Predecessor duration (days), Relationship, Lag days (negative is lead), and Successor duration (days); Hold Successor duration (days) separate from internal buffers.
Instructions
How to use this calculator
Enter predecessor start and duration, relationship type, signed lead or lag, and successor duration.
- Establish Predecessor starts and Predecessor duration (days) as the controlling Dependency Lead/Lag Calculator horizon.
- Establish Relationship, Lag days (negative is lead), and Successor duration (days) from the applicable entered scenario.
- Model the Dependency Lead/Lag Calculator checkpoints, then validate Successor duration (days) in chronological order.
- Verify Successor duration (days) after the other Dependency Lead/Lag Calculator inputs so its separate influence is clear.
Calculation
Method used
The predecessor finish is calculated first. The selected finish-to-start, start-to-start, finish-to-finish, or start-to-finish relationship anchors the successor.
The Dependency Lead/Lag Calculator applies Predecessor starts, Predecessor duration (days), and Relationship in sequence; validate the Successor duration (days) allowance at each checkpoint.
Calculation method last reviewed: June 21, 2026.
Visual audit
Reading the calculated timeline
The Dependency Lead/Lag Calculator timeline models checkpoints from Predecessor starts, Predecessor duration (days), Relationship, Lag days (negative is lead), and Successor duration (days). Validate Successor duration (days) from the anchor toward the horizon carrying the consequence.
Interpretation
Interpreting the calculated date and buffers
The result models one dependency pair. Negative lag represents lead time and can create intentional overlap.
Validate the Dependency Lead/Lag Calculator deadline separately from Successor duration (days); internal buffers remain adjustable unless the entered scenario fixes them.
For a separate check, the Critical Path Timeline Calculator is designed to find the longest dependent task chain and earliest project completion.
Worked scenario
Example calculation
Cross-check the Dependency Lead/Lag Calculator control event with Predecessor starts and Predecessor duration (days), then validate each Successor duration (days) adjustment.
Boundaries
Important edge cases and limitations
Business calendars, partial completion, multiple predecessors, resource limits, and nonworking dates are excluded.
Refresh the Dependency Lead/Lag Calculator allowance when Successor duration (days) differs from the entered scenario rule; model its dependent checkpoints again.
Practical use
Recommended workflow
Confirm relationship semantics in the project plan and test whether overlap is operationally possible.
Input audit
Checklist for this calculation
- Validate the Dependency Lead/Lag Calculator control point in Predecessor starts and Predecessor duration (days).
- Hold Successor duration (days) separate from discretionary buffers.
- Cross-check the earliest Dependency Lead/Lag Calculator checkpoint with its horizon.
- Hold Relationship, Lag days (negative is lead), and Successor duration (days) beside the Dependency Lead/Lag Calculator; include Successor duration (days) in any saved or shared record.
Questions
Frequently asked questions
What is the difference between lead and lag?
Lag inserts waiting time; lead permits the successor to begin before the normal dependency boundary.
Which inputs make a dependency lead/lag calculator result reproducible?
Another reviewer needs Predecessor starts and Predecessor duration (days) and Relationship, Lag days (negative is lead), and Successor duration (days) to recreate the Dependency Lead/Lag Calculator. Store those values with their units and generation date.
What event should trigger another dependency lead/lag calculator calculation?
Reconsider the Dependency Lead/Lag Calculator when Successor duration (days) no longer matches the source used for Predecessor starts. A new calculation keeps the cases separate.
Can an error in Predecessor starts shift the dependency lead/lag calculator output?
Predecessor starts supplies the controlling Dependency Lead/Lag Calculator boundary; Successor duration (days) changes a dependent checkpoint or allowance. Validate that Successor duration (days) allowance before moving the horizon.