Inventory Planning for Online Sellers: A Step-by-Step Guide

What inventory planning actually means

Plan too little and you run out of a best seller, lose the sale and damage your ranking. Plan too much and cash sits on a shelf as slow or dead stock. Inventory planning is the routine that keeps you between those two problems: buy enough, at the right time, of the right things.

It is not forecasting to the decimal. For most small sellers, a handful of numbers per product - how fast it sells, how long it takes to arrive, and how much cushion you want - is enough to make good decisions.

Step 1: Know how fast each product sells

Your sales velocity is the average number of units sold per day (or week). Take the last 30-90 days of sales for each product and divide by the days in that period. If you sold 90 units in 90 days, your velocity is 1 a day.

• Use a period long enough to smooth out one-off spikes, but short enough to reflect current demand.
• Count sales across every channel together. Velocity per channel tells you where demand is, but planning needs the total.
• Ignore unusual days - a viral post, a stock-out that suppressed sales - or at least note them so they do not mislead you.

Step 2: Know your lead times

Lead time is the gap between placing an order with your supplier and the stock being ready to sell. Include production, shipping, customs if relevant, and the time it takes you to receive and check it in. Suppliers often quote a best case - track what really happens over your last few orders and use the realistic number.

Step 3: Set reorder points and safety stock

The reorder point tells you when to buy. The simple version:

Reorder point = (daily sales x lead time in days) + safety stock

Safety stock is the extra cushion for demand running above average or a late delivery. The more variable your sales or your supplier, the more you need.

When stock drops to 76, you place the next order. Use our reorder point calculator and safety stock calculator, or read the longer guides on how to calculate your reorder point, how to calculate safety stock and minimum stock levels. How much to order each time is a separate question - see economic order quantity.

Step 4: Focus effort with ABC analysis

You do not need the same precision for every product. ABC analysis ranks products by how much revenue or profit they bring in: the few "A" items that matter most, a middle group of "B" items, and a long tail of "C" items.

• A items: plan carefully, review often, hold enough safety stock never to run out.
• B items: review monthly with standard reorder points.
• C items: keep lean, reorder in bulk less often, and question whether they earn their shelf space.

Our guide to ABC analysis walks through the calculation. The bottom of the C group is usually where dead stock builds up, and your inventory turnover shows how quickly stock is really moving.

Step 5: Plan for seasons and promotions

Average velocity hides peaks. If a product sells three times as fast in the run-up to Christmas, a reorder point built on yearly averages will leave you short. Look at the same weeks last year, adjust for growth, and buy earlier because peak lead times are often longer. Our guides cover seasonal inventory and Black Friday planning, and inventory forecasting for small businesses goes deeper on the maths.

Step 6: Review on a schedule

A plan that is not revisited goes stale. A workable rhythm:

• Weekly: check what is at or below its reorder point, and place orders.
• Monthly: refresh sales velocity for your A and B items, and look for products that have slowed down.
• Quarterly: review lead times, clear slow stock, and revisit safety stock levels.

Planning across more than one sales channel

Everything above assumes you know how much stock you actually have. Once you sell on eBay, Shopify, Etsy and others, that number splits across shops and drifts out of date, and every plan built on it wobbles. Keep one stock count for each product, and plan from that.

Salync keeps one count and updates your shops automatically, with low-stock alerts, purchase orders and reorder suggestions built around it, so the moment a product hits its reorder point it is flagged rather than noticed at zero. Free for up to 50 products.

Frequently asked questions

What is inventory planning?

Inventory planning is deciding how much of each product to hold and when to reorder, so you avoid both stock-outs and excess stock. It uses sales velocity, supplier lead times and a safety cushion to set reorder points.

How do you plan inventory for an online store?

Work out how fast each product sells across all channels, know your real supplier lead times, set a reorder point with safety stock, focus attention on your best sellers using ABC analysis, plan for seasonal peaks, and review on a regular schedule.

What is the reorder point formula?

Reorder point = (average daily sales x lead time in days) + safety stock. When stock falls to that level, it is time to place the next order.

How often should I review my inventory plan?

Check reorder points weekly, refresh sales velocity monthly for your most important products, and review lead times, slow stock and safety stock quarterly.

What is the difference between inventory planning and inventory control?

Planning decides how much to buy and when. Control is keeping the counts accurate day to day - stock takes, corrections and tracking movements - so your plan is based on real numbers.