Maintenance & Reliability calculator
Spare Parts Reorder Coverage Calculator
Check how long your reorder trigger covers demand after protecting a reserve. Enter the trigger quantity, average withdrawals, reserved stock and replenishment lead time on matching calendars.
What this calculator does
- Compare a spare-part reorder trigger with expected lead-time consumption while retaining an explicit stock reserve.
Formula used
- Usable trigger units = reorder trigger − reserved safety stock
- Protected coverage = usable trigger units ÷ average daily demand
- Gross coverage = reorder trigger ÷ average daily demand
- Expected lead-time demand = average daily demand × replenishment lead time
- Coverage margin = protected coverage − replenishment lead time
Inputs explained
- Reorder Trigger Quantity: Current replenishment trigger from the item’s stocking policy.
- Average Daily Demand: Observed mean daily withdrawals using the same day basis.
- Reserved Safety Stock: Whole units held apart from normal lead-time consumption.
- Replenishment Lead Time: Order-to-available receipt time on the demand calendar.
How to use the result
- Best suited to reorder trigger Review, supplier Lead-Time change.
- Average coverage does not predict stockout probability for intermittent demand. Outstanding orders and allocated stock require a consistent inventory-position policy.
Current U.S. benchmarks
- U.S. manufacturing runs at 75.7% of capacity (Federal Reserve, Aug 2026). New factory orders are up 8.5% year over year (Census).
Common questions
- Is this the physical stock currently on the shelf? Enter the replenishment trigger from your policy. If the policy uses inventory position, treat outstanding orders and allocations consistently.
- Why subtract the reserve first? The reserve protects against variability. Subtracting it shows how much of the trigger can cover normal lead-time demand without consuming that protection.
- Can average demand be zero? No. Coverage in days is undefined without positive demand. Review intermittent-spare requirements using failure history and criticality instead.
- Does a positive margin guarantee no shortage? No. Actual demand and delivery time may exceed their averages. The margin describes expected coverage under the entered values.
Last reviewed 2026-10-06.