Inventory how-to

How to plan inventory when shipping times vary by region

Plan against your slowest reliable shipping lane, not the average.

Short answer: Plan against your slowest reliable shipping lane, not the average. If you ship to several regions from one stock pool, your reorder point should be based on the longest lead time you promise customers, with safety days added for the regions that are less predictable.

Separate supplier lead time from customer shipping time

There are two different clocks here. One is how long it takes your supplier to get stock to you. The other is how long it takes you to get stock to customers in different regions. Inventory planning cares about the first one: supplier lead time plus safety days decides when you reorder and how much. Regional shipping speed affects customer experience and promised delivery dates, but it does not change how much stock you need to hold, unless slow regions also mean slower returns or slower feedback on demand shifts.

Use the worst case lead time for your reorder point

If you hold one pool of inventory that serves multiple regions, set your reorder point using the longest supplier lead time plus a safety buffer, not an average across suppliers or shipping methods. Averages leave you short when the slower link in the chain is the one that actually ships your next restock. If one supplier is reliably fast and another is inconsistent, give the inconsistent one a larger safety day buffer rather than blending the two numbers.

Add safety days for regions with unpredictable customs or carriers

Some regions have more variable customs clearance, carrier delays, or holiday disruption. If demand from these regions makes up a meaningful share of a SKU's sales, increase the safety days for that SKU rather than trying to run per-region stock levels. This keeps the system simple: one reorder point per SKU, sized to cover the worst realistic combination of demand and delay.

Know the limits of single-location planning

If you stock inventory in more than one warehouse or fulfillment center to serve different regions faster, you are now managing per-location demand and transfers between locations. That is a different problem from reorder timing, and it needs separate tracking of what each location is expected to sell and when it needs topping up.

Step by step

  1. List every supplier and their real lead time, not the best case they quoted you.
  2. Identify which regions or shipping methods have the most delay and disruption risk.
  3. Set safety days per SKU based on the slowest reliable path that stock takes to reach you, not an average.
  4. Calculate reorder point as daily sales x (lead time + safety days) using the worst case lead time.
  5. Review actual delivery times every few months and adjust safety days if delays are getting worse or better.
  6. If you stock inventory in multiple locations for different regions, track each location's demand and transfers separately from this process.

Worked example

Say a store sources a product from one supplier with a 20-day lead time to its single warehouse, and that warehouse ships to customers in three regions. One region's deliveries are reliably fast, but a second region often sees customs delays that push effective restock timing out by extra days, so the store sets safety days at 10 instead of 5. Daily sales across all regions for this SKU average 6 units. Reorder point = 6 x (20 + 10) = 180 units. If on hand is 150 and nothing is on order, order quantity using a 14-day cover target would be 6 x (20 + 14) - 150 = 54 units, rounded up to the supplier's case pack.

How SteadyShelf helps

SteadyShelf calculates reorder points and order quantities per SKU using the supplier's lead time and the safety days you set, which covers the "worst case lead time plus buffer" approach described here. It does not forecast demand separately by region or manage stock across multiple warehouses, so if you ship from more than one location to serve different regions, you will need to track that split manually outside the app.

$29/month flat, unlimited products and suppliers, 30-day free trial. Run the numbers now with the free reorder point calculator.

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FAQ

Should I set different safety days for each shipping region?

Not if you hold one stock pool. Set one safety day number per SKU sized to cover the slowest region that matters for that SKU's sales. Splitting safety days by region only makes sense if you also split your inventory by region, which is a separate transfer and multi-location problem.

What if shipping delays are getting worse over time, like during peak season?

Increase safety days temporarily for the affected SKUs and suppliers before peak season starts, based on what you saw happen last year or in recent months. Revert the safety days back down once carrier and customs performance normalizes, so you are not holding excess stock year round for a seasonal problem.

Let SteadyShelf do this math for every SKU

Order-by dates per supplier, seasonal forecasts and draft POs for your Shopify store. $29/month after a 30-day free trial.

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