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Scenario guide

Inventory Runway, Safety Stock and Reorder Planning

Connect inventory days of supply with reorder points and lead-time assumptions without treating forecasts as guarantees.

How to use these calculators

Inventory days of supply answers how long current stock might last at an assumed sales rate. Reorder planning asks an additional question: how much stock will be needed while new goods are in transit? Use the same unit definitions across on-hand inventory, average demand, lead time and safety stock.

A worked scenario

600 units ÷ 25 units sold per day

Estimated inventory coverage: 24 days.

If replenishment takes 18 days and demand rises, reorder earlier; 24 days of coverage is not a 24-day delivery promise.

How to plan this decision

  1. Calculate stock coverage

    Divide sellable on-hand units by representative daily unit sales.

  2. Estimate lead-time demand

    Multiply expected daily demand by the supplier's lead time in days.

  3. Add safety stock

    Allow for demand spikes, missed deliveries and actual service-level requirements.

Read the detailed worked guide →

Start with the formula

Estimate the sales volume needed to cover fixed and variable costs, then stress-test the assumptions.

Read Break-Even Analysis for a New Product or Service →

Recommended tools

Inventory Days of SupplyEstimate how many days your on-hand inventory will last at a chosen daily unit demand rate.Reorder PointEstimate the inventory level that should trigger a replenishment order from demand, lead time, and safety stock.Reorder PointCalculate a basic reorder point using daily demand, lead time and safety stock.Safety StockEstimate safety stock from average and maximum demand and lead time.Inventory TurnoverCalculate inventory turnover from cost of goods sold and average inventory value.