A metro-style critical path with one controlled parallel branchUpdates with every input
Date & Time
Lead Time Timeline Calculator
Build an end-to-end service lead-time network from intake, approval, sourcing, transport, inspection, controlled overlap, and variability, then compare the deterministic path and P90 protection with a promised deadline.
Fully serial duration—
Controlled overlap saved—
Deterministic path duration—
P90 protected duration—
P90 promise slack—
Longest stage—
Parallelized share—
Promise status—
Lead-time dependency network
A metro-style critical path with one controlled parallel branch
Nodes show operational gates, the approval-to-sourcing branch shows overlap, and the P90 terminus is compared with the promise wall.
Stage timing register
Start, finish, dependency, and uncertainty contribution by stage
Audit the end-to-end path rather than relying on one total lead-time number.
| Stage | Duration | Start day | Finish day | Dependency | Path role | Share of P50 |
|---|
Network setup
Enter work and waiting stages as separate durations
- Measure intake and approval independently.
- Use sourcing time from comparable items.
- Enter physical transport and receipt inspection.
- Allow overlap only where work can truly start early.
- Compare the P90 path with the customer promise.
Critical-path logic
Overlap changes dependency timing, not the amount of work
Starting sourcing during approval can shorten the path, but it does not erase either duration.
Variability is applied after the dependency path is calculated so the protection reflects end-to-end observed spread.
Calculation method
Build the dependency path before adding statistical protection
Intake precedes approval. Sourcing may begin during the allowed fraction of approval, then transport and inspection remain sequential. P90 protection is added to the resulting path, not to each stage independently.
Detailed calculation process and general formulas
D_serial=I+A+S+T+RS_start=max(I+A−Ao, I)D₅₀=max(I+A,S_start+S)+T+RD₉₀=D₅₀+1.282σSlack=P−D₉₀Symbols, meanings, and units
- I
- intake durationdays
- A
- approval durationdays
- o
- allowed approval/sourcing overlapdecimal
- σ
- end-to-end duration standard deviationdays
- P
- promised lead timedays
Promise architecture
Separate structural delay from uncertainty protection
The model exposes what is serial, what is deliberately parallel, and what is held as statistical protection.
Serial baseline
—All stages with no overlap.
Dependency benefit
—Days removed by controlled overlap.
Protected path
—P90 end-to-end duration.
Promise margin
—Entered promise less P90 duration.
Decision takeaway: Do not call a shorter path safer unless the remaining promise margin still covers end-to-end variability.
Path checks
Validate dependencies before optimizing them
- Approval may contain hard gates that cannot overlap.
- Transport variability may be non-normal.
- Inspection can trigger rework not modeled here.
- Stage averages must share the same calendar basis.
Timeline evidence
Timestamps that reveal the real critical path
- Request acceptance time
- Approval completion
- Supplier commitment
- Dispatch and receipt scans
- Inspection release timestamp
Practical applications
Decisions this calculator is designed to support
Special-order material
A buyer can begin supplier sourcing after partial technical approval.
What the result clarifies: The network quantifies the true benefit of that controlled overlap.
Service onboarding
A provider promises activation after intake, approval, provisioning, transport, and validation.
What the result clarifies: P90 protection shows whether the published promise is robust.
Worked example
Current-input substitution and reconciliation
Model limitations
The P90 approximation assumes an approximately normal end-to-end duration and one observed standard deviation. The model excludes rework loops, correlated stage delays, working-day calendars, capacity queues, and multiple alternative dependency paths.
Lead Time Timeline Calculator FAQ
Why is P90 larger than P50?
It adds a one-sided 90th-percentile protection term to the deterministic path.
Does overlap reduce stage work?
No. It changes start timing only.
Which stage is critical?
The result identifies the longest entered stage, while the network shows the actual dependency path.
What does negative slack mean?
The P90 protected path exceeds the entered promise.