Aftermarket, Field Service & Service Parts calculator
Service Parts Days of Supply Calculator
Service parts inventory turns and days of supply show whether aftermarket stock is moving fast enough while still protecting customer uptime. This calculator uses on-hand inventory, usage, and safety factor to estimate protected days before replenishment risk increases.
What this calculator does
- Calculate protected days of supply for service parts from inventory on hand, daily usage, and safety-stock factor.
- a parts inventory analyst needs to understand how long current service stock will support demand
- Returns protected days of supply for service-parts inventory.
Formula used
- Unprotected days of supply = on-hand service parts inventory ÷ average daily usage
- Protected days of supply = unprotected days of supply ÷ safety factor
Inputs explained
- Service parts inventory on hand: undefined
- Average service parts usage: undefined
- Demand and lead-time safety factor: undefined
How to use the result
- Use it for high-runner parts, regional stocking, dealer inventory, replenishment reviews, and obsolete stock reduction.
- It does not replace SKU-level forecasting; intermittent demand, supersessions, minimum buys, and supplier lead times can change stocking decisions.
Common questions
- What information do I need for service parts days of supply? You need on-hand inventory, average daily usage, and a safety factor for demand or lead-time variability.
- Which units or time period should I use for service parts days of supply? Use the units shown next to each input and keep all counts, costs, service calls, installed-base records, and labor hours in the same planning period. Convert mixed periods such as weeks, months, quarters, or years before entering the values.
- What does the service parts days of supply result tell me? It estimates how many protected days current service-parts inventory can cover.
- When is this service parts days of supply estimate only approximate? Use it to trigger replenishment, redistribute stock, reduce excess, or revise min/max levels.
Last reviewed 2026-05-12.