How Replenishment suggests your reorder date and quantity
The reorder quantity is the number of units Sumtracker suggests you buy so the product stays in stock for your chosen days of cover, starting from the day it becomes out of stock.
Sumtracker works this out for every product in every warehouse. It looks at three things:
- How fast the product sells, predicted from your last 12 months of sales.
- How much stock you have, after subtracting units already promised to open orders.
- What is already on the way, from purchase orders and stock transfers marked as incoming.
Alongside the quantity, Sumtracker also shows a reorder date: the last day to place the order so it arrives in time. The numbers refresh automatically every few hours, so you never need to recalculate them yourself.
The terms you will see
Four settings shape the suggestion.
Settings you control
| Term | What it means | Where it is set |
|---|---|---|
| Days of cover | How many days of sales one order should last. 30 means "buy enough for about a month". | On the product, or the account default when the product has none. Allowed range is 7 to 180. |
| Lead time | How many days pass between placing an order with your supplier and the stock arriving in your warehouse. | On the product's primary supplier, or the account default. Allowed range is 1 to 180. |
| Safety days | Extra days added as a cushion against late deliveries or a sudden rush of orders. They make you order earlier, not order more. | On the product's primary supplier, or the account default. Allowed range is 0 to 60. |
| Busy months | Up to 3 calendar months you name as your peak season, such as November and December. | Account replenishment settings. |
When a setting exists in more than one place, the most specific one wins: the product first, then the supplier, then the account default.
How the calculation works
Sumtracker answers four questions in order, separately for each product in each warehouse.
Stock you already have, plus deliveries already ordered, carries you to the stock-out date. The reorder quantity pays for the days of cover after it.
1. How much will I sell each day?
Sumtracker looks back over the last 365 days of sales and predicts sales for each of the next 12 months. A few rules keep the prediction fair:
- Only in-stock days count. If the product was sold out for two weeks, those weeks do not drag its sales rate down.
- Recent sales move the prediction. If the last 3 months sold faster or slower than the year as a whole, future months are adjusted up by at most 50% or down by at most 30%.
- Busy months are kept apart. A month you named as busy is predicted from how it sold last time, and it does not inflate your quiet months.
- This month blends actuals and pace. It is what has sold so far, plus the recent daily pace for the days left.
- New products need some history. No prediction is made until the product has at least 14 in-stock days of sales history.
Sales mean units ordered by customers from that warehouse, minus cancellations. When a bundle sells, the sale counts towards each product inside it. Each month's prediction is then spread evenly over its days to give a daily sales rate.
2. When will I run out?
Starting from today's available stock, Sumtracker steps forward one day at a time. Each day it adds any delivery due that day and subtracts that day's predicted sales. The first day stock reaches zero is the stock-out date.
If the product is already out of stock and a delivery is on the way, the wait for that delivery is skipped. The stock-out date becomes the day you would run out again after it lands, since nothing ordered today can arrive sooner anyway.
3. When must I order?
Count back from the stock-out date by your lead time, then by your safety days:
Reorder date = Stockout date - Lead time - Safety days
An order placed on that day arrives with the safety days still left on the shelf, as a cushion if the supplier is late or sales spike.
4. How much should I order?
The stock you already have carries you to the stock-out date, so the order only has to cover the days after it:
Reorder quantity = Predicted sales over the days of cover - Deliveries already due in that period
Cover starts on the stock-out date itself, the first day with no stock, and runs for your days of cover after it. The result is rounded up to a whole unit.
If today is already past the reorder date, the order arrives late and eats into your cushion. To make up for it, the cover period is stretched by one day for each day late, up to your safety days.
Worked example
A linen tote bag needs 124 units ordered by 9 April. Here is how Sumtracker gets there.
| What Sumtracker knows on 1 March | Value |
|---|---|
| In stock | 230 units |
| Promised to unshipped orders | 30 units |
| Available stock | 200 units |
| Incoming purchase order | 40 units, due 11 March |
| Predicted sales | 4 units a day (124 in March, 120 in April, 124 in May) |
| Lead time, from the supplier | 14 days |
| Safety days, account default | 7 days |
| Days of cover, account default | 30 days |
- Stock-out date: 30 April. 200 available plus 40 arriving makes 240 units. At 4 a day they last 60 days from 1 March.
- Reorder date: 9 April. That is 30 April minus 14 days of lead time minus 7 safety days.
- Reorder quantity: 124 units. Cover runs from 30 April, the first day with no stock, for 30 more days to 30 May. That is 31 days × 4 units. The 40 units due 11 March land before the stock-out date, so they already pushed that date later and are not subtracted again.
What changes the answer
- The delivery slips to 10 May. The bag now runs out on 20 April, so the reorder date moves up to 30 March. The 40 units land inside the cover period, so the quantity drops to 124 − 40 = 84.
- You order late, on 12 April. That is 3 days past the reorder date, so cover stretches by 3 days: 34 days × 4 = 136 units.
- You raise days of cover to 60. Cover becomes 61 days × 4 = 244 units. The reorder date does not move.