How to plan your stock around delivery days

Many mini-marts and small shops in Jamaica and the wider Caribbean get deliveries only once or twice a week. If a product runs out on Wednesday and the distributor comes on Monday, that shelf is empty for five days, no matter how nicely you ask.

The usual advice on reorder points assumes you can order whenever you like and the stock arrives after a few days. With a fixed delivery day, that is not how it works. You do not order when you hit a number. You order on the day the rep calls, or before the cutoff, and then you wait for the next truck. That changes what lead time means and how much you need to order.

Suppose your distributor's rep visits every Monday, takes your order and delivers on Wednesday. If you realise on Tuesday that you are low on something, you cannot do anything until next Monday, and the stock arrives the Wednesday after. That is nine days from noticing to shelf.

The simplest way to plan around this is to stop thinking about "when do I run low" and start thinking about "what has to last until the next delivery". At the moment you place an order, the next chance to fix a mistake is a full cycle away. So the order you place must cover:

• the days between now and when this order arrives,
• the days after it arrives until the following delivery,
• and a cushion for a busy week or a late truck.

This is a lead time calculation where the wait is set by the calendar, not by the supplier's speed.

A mini-mart sells about 5 cases of bottled water a week, which is 60 bottles across 6 trading days, so 10 bottles a day. The distributor takes the order on Monday and delivers on Wednesday, and visits again the next Monday. Water comes in cases of 12.

1. Set the lead time

   Order Monday, arrives Wednesday: 2 days of waiting. Then the delivery has to last until the Wednesday after, which is 7 days between deliveries. Total cover needed: 9 days.

2. Work out demand over that time

   10 bottles a day x 9 days = 90 bottles.

3. Add safety stock

   Your busiest day last month was 16 bottles, 6 above normal. Using the busiest-day method over 9 days is 54 extra, which is too heavy for a cheap, bulky product. Use 2 days of cover instead: 20 bottles.

4. Set the order-up-to level

   90 + 20 = 110 bottles.

5. Order the difference

   On Monday you count 40 bottles on hand. 110 - 40 = 70 bottles. Water comes in cases of 12, so round up to 6 cases (72 bottles).

Check that it works. You hold 40 on Monday and sell 20 before Wednesday's truck, leaving 20. The delivery adds 72, so you have 92. By the next Monday, five more days of sales leave you with about 42, so you count, order 6 cases again (110 - 42 = 68, rounded up to 72), and by the Wednesday after you are down to about 22, which is your cushion.

Notice that a standard reorder point of "10 bottles a day x 2 days lead time = 20" would be misleading here. Hitting 20 on a Thursday would not help, because the next order cannot be placed until Monday. The delivery cycle is what matters.

What if you only count a minimum?

If you prefer a per-product minimum, set it to cover the gap until the next order day. In this example, that is the cushion plus enough to last from a Tuesday until Monday's order arrives. Set the minimum for the full cycle, and checking the shelf the day before the rep arrives becomes quick: anything under its minimum goes on the order.

The same method works for any rhythm. Only the days between deliveries change.

Longer cycles mean bigger orders, more cash tied up and more shelf and storage space. If a fortnightly supplier is the only one for a product that sells fast, check whether your storage can hold 180 bottles. If it cannot, you have two choices: find a second source for part of your demand, or accept some stock-outs and price the product accordingly. Read cash flow for shop owners before you commit to large fortnightly orders.

Most shops have more than one supplier, each with their own day. A typical week might look like this.

Give each supplier its own list and its own cutoff, and check stock for that group the evening before. This stops the commonest mistake: counting everything at once on a random day and ordering the wrong things from the wrong people. A restock list grouped by supplier makes it easy.

Overlap helps, too. If two suppliers carry the same product, a product that runs short on one run can sometimes be covered by the other. Note which products have a second source, so a stock-out on the first does not turn into a week-long gap.

• Public holidays. A Monday holiday can shift a whole route a day or more. Ask the rep for the holiday schedule and order extra for the longer gap.
• Heavy rain and bad roads. Late trucks are common in some parishes. Keep a larger cushion on essentials.
• Busy weeks. Payday weekends, school openings and festivals lift sales. See how to plan for busy season.
• Missed cutoff. Know the rep's cutoff time. Missing it by an hour can cost a week.

• Using the supplier's quoted delivery time as lead time. Your real lead time includes the wait for the next visit.
• Ordering only what you are out of today, rather than what must last until the next delivery.
• Counting stock the morning of the rep's visit with no time to check the back room.
• Forgetting that a late or short delivery leaves you a whole cycle without that product. See short, damaged or substituted deliveries.
• Never reviewing the numbers when sales change.

Set a low-stock minimum for each product, sized to cover the gap between deliveries, and Shopkeepa sends one reminder when stock crosses it. The product then joins your restock list with a suggested order quantity, so on the day before the rep visits you can see at a glance what needs ordering.

Because Stock In records what actually arrived, the numbers stay honest cycle after cycle, and best sellers and slow movers reports show where your quantities need to go up or down. Learn more about low-stock reminders. Shopkeepa does not place orders for you. Shopkeepa is in development, and early access shops will help shape it.