Overview
Lead time is the delay between placing a purchase order and receiving sellable stock. Underestimating it is one of the fastest ways to create stockouts and lost revenue. Overestimating it can push you into overstock. A structured approach that combines average lead time, variability, and safety stock lets you reorder on time even when suppliers run late.
Measure actual lead times, not promised ones
Start by tracking ordered and received dates in Admin → Purchase orders so you can calculate real lead times for each supplier, not just the quoted number. For overseas manufacturers, expect variance of around 20–30% and confirm whether your data matches that benchmark before setting reorder rules.
Bake lead time into reorder points
Use the reorder point formula and calculator at /calculators/reorder-point-calculator, which multiplies average daily demand from Shopify Analytics → Sales by product by lead time days. This ensures you place a PO one full lead time before you will run out under normal demand conditions.
Layer safety stock on top of lead time demand
Because demand and lead time both fluctuate, use the safety stock calculator at /calculators/safety-stock-calculator to target a 95% in-stock service level. The safety stock formula explicitly captures volatility so that a late container or a spike in sales does not immediately cause a stockout.
Address changing lead times before Stocky ends
Stocky, Shopify's native inventory planning app, is being discontinued on August 31, 2026, so any lead time assumptions you have stored there will effectively disappear. Synplex keeps lead time history and variance per supplier and SKU so your reorder logic stays robust long after Stocky is shut down.
Worked examples
Electronics brand importing from an overseas supplier
- Average daily sales: 50 units
- Average lead time: 30 days
- Lead time variance: ±20%
- 1. Use Shopify Analytics → Sales by product to confirm average daily sales of 50 units.
- 2. Multiply 50 units by 30 days to get 1,500 units of lead time demand.
- 3. Use /calculators/safety-stock-calculator to add safety stock based on 20% lead time variance and your target 95% service level.
Result: You set a reorder point equal to 1,500 units of lead time demand plus calculated safety stock, and reorder whenever projected stock moves below that threshold.
This method turns fuzzy lead time estimates into a clear reorder rule that tolerates routine delays without constant stockouts.
How to apply this in Shopify
Record expected and actual receipt dates on every line in Admin → Purchase orders to build a lead time history per supplier.
Use Shopify Analytics → Reports → Inventory to see how current on-hand and inbound POs translate into days of supply at existing lead times.
When lead times shift, adjust reorder points in your planner and then cross-check them with current on-hand in Admin → Products → Inventory.
Use Admin → Transfers to separate supplier lead time from internal warehouse transfer time when stock moves between locations.
Turn on low stock alerts under Admin → Settings → Notifications → Low stock alerts based on calculated reorder points rather than arbitrary thresholds.
Common mistakes
Using quoted lead times instead of actual data
Relying on a supplier’s promised lead time instead of measured history causes you to underestimate delays and run out of stock.
Fix: Track ordered versus received dates in Admin → Purchase orders and feed actual averages and variance into your reorder point calculation.
Ignoring lead time variability
Assuming a fixed number of days when actual lead time varies by around 20–30% leaves no buffer for routine delays.
Fix: Use safety stock with a 95% service level benchmark via /calculators/safety-stock-calculator to absorb typical fluctuations.
Hardcoding lead times in Stocky
Storing lead time assumptions only in Stocky means your data disappears when the app is discontinued in August 2026.
Fix: Export lead time history now and import it into Synplex so your reorder math continues to respect accurate lead times.
Frequently asked questions
Related resources
Related questions
- When should I reorder inventory?
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- How do I forecast inventory demand?
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Related calculators
- Reorder Point Calculator for Shopify Brands | Free ROP Formula
Calculate the exact reorder point for every SKU. Use the free Synplex reorder point calculator with worked examples, safety stock integration, and Shopify-specific tips.
- Safety Stock Calculator for Shopify Brands | Free Formula + Tool
Calculate your ideal safety stock level instantly. Use the free Synplex safety stock calculator to protect against stockouts, understand Z-values, and see worked examples for Shopify inventory planning.