Daily arrivals and protected completions shaping the backlog waterlineUpdates with every input
Date & Time
Lead Time Schedule Calculator
Project backlog and lead time across a daily operating horizon using starting work, new arrivals, focused service capacity, setup loss, and protected reserve capacity.
Protected weekday capacity—
Protected weekend capacity—
Peak backlog—
Ending backlog—
First backlog-clear day—
Average implied lead time—
Demand-to-capacity utilization—
Schedule status—
Queue tide chart
Daily arrivals and protected completions shaping the backlog waterline
The filled curve tracks backlog while paired daily columns compare incoming work with weekday and weekend service capacity.
Daily queue schedule
Arrival, completion, backlog, and implied lead-time ledger
Follow daily capacity by weekday, new arrivals, completed work, ending backlog, utilization, and implied customer lead time.
| Day | Day type | Arrivals | Protected capacity | Completed | Ending backlog | Implied lead time |
|---|
Schedule setup
Use protected capacity, not the best observed day
- Start with all currently waiting work.
- Use a sustainable daily arrival rate.
- Reduce capacity for setup and reserve.
- Model weekend capacity explicitly.
- Choose a horizon long enough to reveal stability.
Queue logic
Backlog clears only when cumulative protected capacity outruns cumulative demand
A weekday surplus can be erased by low-capacity weekends, so the schedule rolls through each day type rather than multiplying one average.
Implied lead time divides the current queue by that day's protected service capacity, making congestion visible.
Calculation method
Roll backlog forward using protected daily service capacity
Setup loss and reserve reduce nominal capacity. Weekend capacity is scaled separately. Each day's completion cannot exceed work available.
Detailed calculation process and general formulas
Cap_w=C(1-s)(1-r)Cap_e=Cap_w f_eB_t=max(B_(t-1)+A-C_t,0)Done_t=min(B_(t-1)+A,C_t)Lead_t=B_t/max(C_t,ε)Symbols, meanings, and units
- C
- nominal daily capacityunits/day
- s
- setup-loss sharedecimal
- r
- protected reserve sharedecimal
- A
- new daily arrivalsunits/day
- B_t
- backlog after day tunits
Queue stability
Distinguish temporary backlog from structural overload
The chart shows whether the backlog slopes toward zero, stabilizes, or grows through the planning horizon.
Weekday engine
—Capacity after setup loss and reserve.
Weekend engine
—Scaled protected capacity on weekend days.
Peak queue
—Largest backlog reached in the horizon.
Horizon exit
—Work still waiting after the final day.
Decision takeaway: A queue can look manageable on weekdays yet remain unstable when protected weekend capacity is too low.
Queue checks
Validate arrival and capacity behavior
- Arrivals may vary by weekday.
- Capacity may be shared with priority work.
- Setup losses can depend on product mix.
- Reserve should cover real disruption, not arbitrary padding.
Schedule evidence
Data needed to maintain the projection
- Backlog snapshot
- Daily arrival history
- Completed-unit history
- Setup and changeover loss
- Weekend staffing calendar
Practical applications
Decisions this calculator is designed to support
Service request queue
A support operation has weekday specialists and a small weekend crew.
What the result clarifies: The tide chart shows whether Monday backlog is structural or temporary.
Production order book
Daily orders arrive while setup and reserve reduce nominal output.
What the result clarifies: The schedule identifies the first clear day and the residual horizon backlog.
Worked example
Current-input substitution and reconciliation
Model limitations
This deterministic queue model assumes constant arrivals, fixed weekday/weekend patterns, and no priority classes. It excludes random arrivals, service-time distributions, cancellations, due-date sequencing, and multiple shared resources.
Lead Time Schedule Calculator FAQ
Why protect capacity with reserve?
Reserve prevents the schedule from consuming every nominal unit of capability.
Can backlog clear and return?
Yes when later arrivals exceed that day's protected capacity.
How is implied lead time calculated?
Ending backlog is divided by the day's protected capacity.
What does an unstable status mean?
The backlog remains positive and demand utilization is at or above sustainable capacity.