Automating purchase orders based on reorder points
Replenishment in ecommerce often depends on timely purchase orders that reflect real demand and supplier lead times. When reorder points are applied consistently and purchase orders are raised automatically, stock availability is easier to maintain without constant manual checking.
By Sean SaleUpdated
Co-founder of Just Applications Ltd, the team behind Adlixor
The Challenge
Manual purchase ordering usually relies on spreadsheets, periodic stock reviews, and individual judgement, which can miss sudden demand changes and lead-time variability. This creates stockouts, over-ordering, and rushed despatch decisions, while also making it difficult to explain why an order was placed or delayed.
The Solution
A systematic approach sets reorder points and reorder quantities per SKU using sales velocity, lead time, and safety stock, then generates draft or approved purchase orders when thresholds are reached. Automated triggers keep ordering aligned to current inventory positions, open sales orders, and inbound stock, producing a repeatable audit trail and reducing avoidable exceptions.
Step-by-Step Guide
- 1
Define which SKUs are eligible for automated replenishment and which require manual review due to seasonality, MOQs, or supplier constraints.
- 2
Clean and standardise supplier records, lead times, pack sizes, minimum order quantities, and ordering calendars.
- 3
Calculate baseline demand (e.g. average daily units) using a consistent historical window and separate out promotions and one-off events.
- 4
Set reorder points per SKU using lead time demand plus safety stock, and agree the service level target that safety stock should protect.
- 5
Set reorder quantities using a defined policy such as economic order quantity, days-of-cover targets, or supplier pack multiples.
- 6
Ensure the inventory position used for triggers includes on-hand, reserved, inbound purchase orders, and any quarantined or unsellable stock.
- 7
Configure the purchase order trigger to create a draft PO when inventory position falls below the reorder point, grouped by supplier and warehouse where relevant.
- 8
Add approvals and exception rules for price changes, unusual quantities, new SKUs, or supplier lead-time breaches.
- 9
Monitor outcomes weekly and adjust reorder points and safety stock based on forecast error, supplier performance, and changes in demand.
Pro Tips
- ✓Use different lead times for normal supply versus peak periods if suppliers reliably behave differently across the year.
- ✓Exclude cancelled orders and returns from demand calculations unless they represent a consistent proportion of sales for that SKU.
- ✓Treat bundles carefully by exploding bundle demand into component SKUs so components replenish correctly.
- ✓Cap automated order quantities for slow movers to avoid tying cash up in long tail stock.
- ✓Review reserved stock logic so backorders and pre-orders do not cause double counting against available inventory.
- ✓Log every automated PO decision with the inputs used, including stock on hand, inbound quantity, lead time, and safety stock.
Frequently Asked Questions
- What is a reorder point in ecommerce purchasing?
- A reorder point is the inventory position threshold that triggers replenishment. It is typically calculated as expected demand during supplier lead time plus a safety stock buffer.
- What data is required to automate purchase orders reliably?
- At minimum you need accurate on-hand stock, reserved stock, open sales orders, inbound purchase orders, supplier lead times, and SKU-to-supplier mappings. Better results come from clean historical sales data and defined MOQ, pack sizes, and ordering cadence.
- How do safety stock levels affect automation outcomes?
- Higher safety stock reduces stockouts but increases inventory holding and cash tied up. Lower safety stock reduces holding cost but increases the frequency and impact of stockouts when demand spikes or suppliers slip.
- Should automated POs be created automatically or as drafts for approval?
- Draft creation with approval is usually safer during the initial rollout and for SKUs with volatile demand. Fully automatic approval can work for stable, high-volume items once thresholds and exception rules are proven.
- How do you avoid over-ordering when there is inbound stock?
- Base the trigger on inventory position rather than on-hand stock, subtracting reservations and adding inbound quantities that are confirmed. If inbound POs are frequently late, consider only counting inbound after a supplier has confirmed shipment dates.
- How often should reorder points be recalculated?
- Many teams review weekly or monthly depending on SKU velocity. Recalculate more frequently for fast movers and during periods of demand change, and less frequently for slow movers where noise dominates the signal.
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