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Lead Time & the Reorder Point

Lead time is the number of days between placing a purchase order and receiving the stock. It is one of two inputs to the reorder point calculation — the other being buffer stock days. Together they determine how early the simulation flags a variant for reorder.

For the full reorder point formula, see Buffer Stock & the Reorder Point. This article covers where lead time is configured, how it flows into the simulation, and how to set it accurately.

How lead time is used in the simulation​

The simulation uses leadTimeDays in two places:

  1. Reorder point — stock is flagged when the simulation projects it will fall to: reorderPoint = avgDailyDemand × (leadTimeDays + bufferStockDays)

A longer lead time raises the reorder point, causing Low Stock to fire earlier.

  1. Virtual order scheduling — when the simulation triggers a virtual purchase order, the stock from that order is added to the simulation on day + leadTimeDays. This is how the 12-month supply plan knows when replenishments will arrive.

The default lead time is 30 days if no supplier product record is configured.

Where lead time is configured​

Supplier product record (primary)​

Lead time is set per supplier product record — the link between a specific variant and a specific supplier. Navigate to a variant in the inventory table, open the product detail page, and go to the Suppliers tab. Each supplier product record has its own leadTimeDays field.

This is the value the simulation uses for that inventory level. If a variant has multiple supplier product records, the simulation uses the lead time from the record associated with the active procurement strategy for that inventory level.

Shop default​

Go to Settings → Insight Settings and set the Default Lead Time Days field. This is the fallback used when an inventory level has no supplier product record with a lead time set.

SettingDefaultEffect
Default Lead Time Days (defaultLeadTimeDays)30 daysUsed when no per-level lead time is configured

Per-inventory-level override​

Individual inventory levels (variant × location) can have their own lead time override, set on the product detail page. Use this when a specific location sources from a supplier with a materially different lead time than the rest of your network.

Setting lead time accurately​

Lead time in Synplex is a single fixed number of days per supplier product record. The simulation does not automatically track historical delivery performance or calculate variance — you are responsible for keeping the value current and realistic.

How to determine the right value:

  • Look at your past purchase orders for this supplier. Calculate the average number of days between order placement and stock receipt across the last 5–10 orders.
  • If delivery times are variable, use a value closer to the 75th–90th percentile of actual delivery times rather than the average — or increase buffer stock days to absorb the variability instead.
  • If your supplier has different lead times by season (slower during peak periods, faster off-season), update the value before the season changes.

When to update:

  • After a supplier changes their fulfilment process or shipping partner
  • After observing a sustained shift in actual delivery times
  • Before a known peak season that typically slows your supplier down

How lead time interacts with buffer stock days​

Both settings raise the reorder point when increased. They protect against different things:

SettingProtects againstWhere to increase it
leadTimeDaysOrders taking longer to arrive than expectedWhen actual delivery times are longer than your current setting
bufferStockDaysDemand running above plan during the lead time windowWhen you are experiencing stockouts even with accurate lead times

Increasing lead time is the right lever when the problem is delivery timing. Increasing buffer stock days is the right lever when deliveries arrive on time but demand spikes cause stockouts during the wait.

Do not compensate for a poorly set lead time by inflating buffer stock days, and vice versa — each setting has a distinct purpose and affects the simulation differently.

Effect on the Low Stock status​

The Low Stock status fires when daysUntilReorder — the number of days until the simulation projects stock will hit the reorder point — falls to or below defaultRunningLowDays (default: 40 days). This threshold is configured separately in Settings → Insight Settings.

A longer lead time raises the reorder point, which means daysUntilReorder reaches the Low Stock threshold sooner — giving you more calendar time to act before the reorder point is actually hit. This is intentional: the alert is designed to fire early enough that you have time to place and receive an order.