Days of cover and reorder quantities, worked through
How to turn sales velocity into days of cover and a reorder quantity that respects lead time, safety buffer, minimum order quantities and case packs.
Stokrio Team · · 6 min read
Most reorder spreadsheets answer one question badly: "do we need more?" A better question is "how many days will what we have last, and how much do we need to cover the time until the next delivery?" This guide works through the arithmetic step by step.
Start with daily velocity
Daily velocity is the number of units sold per day over a recent window:
daily velocity = units sold in the window ÷ days in the windowThe window is a trade-off. Seven days reacts quickly to change but is noisy; ninety days is stable but slow to notice a trend. Thirty days is a common default for steady products. Use a shorter window for fast-moving or newly launched products.
Days of cover
Days of cover tells you how long current and incoming stock will last at the current rate of sale:
days of cover = (on hand + on order) ÷ daily velocityInclude stock on open purchase orders that a supplier has confirmed. Leave out draft orders you haven't sent — they aren't coming yet.
The reorder target
You need enough stock to cover the supplier's lead time, plus a buffer for the unexpected:
target = (lead time days + safety buffer days) × daily velocityThe suggested order is whatever is missing from that target:
suggested quantity = target − (on hand + on order)If the result is zero or negative, you don't need to order yet.
Minimums and case packs
Suppliers rarely sell single units. Apply their constraints after you work out the need:
- If the suggestion is below the supplier's minimum order quantity (MOQ), raise it to the MOQ.
- Round up to a whole number of cases.
A worked example
| Input | Value |
|---|---|
| Units sold in the last 30 days | 600 |
| On hand | 420 |
| On order | 180 |
| Supplier lead time | 21 days |
| Safety buffer | 14 days |
| MOQ | 200 |
| Case pack | 48 |
- Daily velocity = 600 ÷ 30 = 20 per day
- Days of cover = (420 + 180) ÷ 20 = 30 days
- Target = (21 + 14) × 20 = 700 units
- Gap = 700 − 600 = 100 units
- Raised to the MOQ: 200 units
- Rounded up to cases: ⌈200 ÷ 48⌉ = 5 cases = 240 units
With 30 days of cover and a 35-day target, this SKU should be reordered now.
When the numbers mislead
- No recent sales. A SKU with zero velocity has infinite cover. That's a signal to check whether it is discontinued, out of stock, or new — not a reason to order nothing forever.
- Stockouts in the window. Days with no stock to sell drag velocity down. See stockout-adjusted velocity.
- Missing costs or suppliers. Without a lead time you can't set a target, and without a cost you can't value the order. Fix the data rather than guessing.
In Stokrio
Stokrio goes a step further than a single velocity window: each product's forecast comes from a model chosen by backtesting its own history, and the reorder point uses statistical safety stock and each supplier's measured lead time. Days of cover still includes open purchase orders, and suggestions are rounded to MOQs and case packs exactly as above. See replenishment.