How to manage inventory for a small business, without complex software

What inventory management actually means

For a small business, inventory management comes down to three questions: what do I have, what is selling, and when should I reorder (and how much)? Get them right and you avoid two expensive mistakes. A stockout sends a customer to your competitor. Overstock ties up cash in products that expire, go out of fashion or simply sit there.

With a few dozen or a few hundred products, you don’t need an enterprise system. A notebook, an inventory spreadsheet or a phone app will do, as long as you apply the same rules every time. The vocabulary you need:

Step 1: one stock card per product

The stock card is the foundation. It holds the fixed details of a product and, underneath, every movement. Here is a template you can copy into a notebook or spreadsheet, filled in for a phone accessories shop.

STOCK CARD
Item: USB-C wall charger 20W         SKU: CHG-20W
Supplier: ____________               Lead time: 7 days
Unit cost: $6.00                     Selling price: $15.00
Average sales: 3 per day             Safety stock: 14
Reorder point: 35                    Usual order: 48 (4 cases of 12)

Date       | Movement                  |  In | Out | On hand
Oct 1      | Opening stock             |     |     |   58
Oct 1-7    | Sales (7 days)            |     |  23 |   35  <- reorder point: order now
Oct 7      | Order placed: 48 units    |     |     |   35
Oct 8-13   | Sales (6 days)            |     |  19 |   16
Oct 14     | Delivery ($6.50/unit)     |  48 |     |   64
Oct 14     | Damaged in transit        |     |   1 |   63
Oct 15-18  | Sales (4 days)            |     |  12 |   51
Oct 18     | Count: 49 on the shelf    |     |   2 |   49  gap: -2
__________ | _________________________ | ___ | ___ | _____

In a spreadsheet, use two tabs. Products holds one row per SKU. Movements holds one row per stock-in or stock-out, with date, SKU and quantity. Stock on hand then calculates itself: opening stock + total in − total out, using a SUMIF per SKU. Add conditional formatting that turns the cell red when stock falls to the reorder point.

Step 2: record every movement, the same day

Accurate stock depends on one habit: nothing comes in or goes out without being written down. The movements to track:

• deliveries (check them against the packing slip before you sign);
• sales, as they happen or at close;
• damaged, expired or unsellable items;
• customer returns and returns to suppliers;
• anything you take home for personal use. It is a stock-out like any other, or both your stock and your margins will be wrong. Our guide to separating personal and business records covers this in detail.

Step 3: calculate your reorder point and safety stock

The reorder point answers “when do I order?”. The basic formula:

Reorder point = average daily sales × lead time (days) + safety stock

The charger sells 3 a day on average and takes 7 days to arrive, so you need at least 21 on the shelf when you order. Safety stock covers the days you sell more, or the supplier who delivers late. Three ways to set it, from simplest to most precise:

1. Peak method: (peak daily sales − average daily sales) × lead time. On busy days the shop sells 5: (5 − 3) × 7 = 14. Reorder point: 21 + 14 = 35.
2. Max–average method: (max daily sales × max lead time) − (average daily sales × average lead time). If the supplier sometimes takes 10 days: 5 × 10 − 3 × 7 = 50 − 21 = 29. Reorder point: 50. It also protects you against late deliveries, but the Institute for Supply Management warns it can overstate the buffer when a few unusual days skew the data.
3. Statistical method: Z × standard deviation of daily sales × √lead time. To avoid a stockout in 95% of order cycles, Z = 1.65. With a standard deviation of 1.2 chargers a day: 1.65 × 1.2 × √7 ≈ 5.2, rounded up to 6. Reorder point: 27. You need a few weeks of recorded sales to get the standard deviation (STDEV in any spreadsheet).

Safety stock is not the same as minimum stock. The first is a buffer for surprises; the second (your reorder point) also includes normal sales during the lead time.

Step 4: decide how much to order

A simple rule: order enough to last until your next order, plus the lead time, plus safety stock, minus what you still have.

Order quantity = average daily sales × (days between orders + lead time) + safety stock − stock on hand

The shop orders every two weeks: 3 × (14 + 7) + 14 − 35 = 42, rounded up to 48 to match cases of 12. Then adjust for real-world limits: supplier minimums, volume discounts, shelf space, expiry dates and, above all, cash.

Step 5: sell the oldest stock first (FIFO)

First in, first out is first of all a physical habit: new deliveries go to the back, older stock to the front. For anything with a date (food, cosmetics, batteries), use “first expired, first out”: the expiry date decides, not the arrival date.

FIFO is also a costing method. Under international standards (IAS 2), interchangeable items are costed with FIFO or weighted average cost; LIFO (last in, first out) is prohibited. US GAAP still permits LIFO, though most companies use FIFO or weighted average. In the example, 16 chargers remained at $6.00 when 48 arrived at $6.50. The weighted average cost becomes (16 × $6.00 + 48 × $6.50) ÷ 64 = $408 ÷ 64 = $6.375.

For tax, the IRS says an inventory is needed to clearly show income when producing, buying or selling merchandise earns you money, with simpler options for qualifying small businesses. Your accountant can tell you which applies to you.

Step 6: rank your products with ABC analysis

Not every product deserves the same attention. ABC analysis, described in 1951 by H. Ford Dickie at General Electric, ranks SKUs by their share of yearly spend or sales. Here is the shop’s year, at cost:

Three SKUs out of ten account for 77% of the value. Those are the ones you never let run out, count most often and negotiate hardest on. C items can be managed loosely: a slightly bigger buffer, an occasional bulk order. The 80/15/5 cut-offs you often see are rules of thumb, not laws.

Step 7: count regularly

There are three ways to organise stock counts:

• Perpetual inventory: every movement is recorded, so the card shows stock at any moment. That’s what the stock card above does.
• Periodic inventory: you count everything on a set date (month end, year end) and work out sales from the difference. Simple, but you discover problems late.
• Cycle counting: you count part of the stock every week. For example, A items weekly, B items monthly, C items quarterly.

Counting rules that help: count with the doors closed, before logging a new delivery; count A items in pairs; and write down the number you count before looking at the card, so it doesn’t influence you.

Shrinkage: the gap that costs money

On October 18 the card says 51 chargers; the shelf holds 49. Two have gone: 2 × $6.375 = $12.75 of shrinkage on one SKU. Record the gap as a stock-out so the card restarts from reality, then look for the cause.

These figures come from 177 US retail brands surveyed by the National Retail Federation, not from small shops. Still, they show that more than a quarter of losses come from mistakes: unchecked deliveries, unrecorded breakage, sales keyed in wrong. Those are the easiest to fix. The NRF stopped publishing this annual survey in 2024.

Inventory and cash flow

Every item on the shelf has already been paid for. The longer it sits, the longer that cash is unavailable for anything else. Two standard ratios:

• Inventory turnover = cost of goods sold ÷ average inventory at cost.
• Days of inventory = 365 ÷ inventory turnover.

If the shop’s cost of goods sold is $36,000 a year and it holds $9,000 of stock on average, turnover is 4, and an item takes about 91 days to sell. Flag every SKU that hasn’t moved in 90 days: discount it, bundle it with an A item, or return it if your supplier agreement allows.

Track margin per product too. A charger sold at $15.00 with an average cost of $6.375 earns $8.625: a gross margin of 57.5% of the selling price, or a markup of about 135% on cost. A fast seller with a thin margin can earn more than a high-margin item gathering dust.

Market stalls and online sellers

On a market stall, logging every sale is hard. Count at the start and end of the day instead: units sold = morning stock + restock − evening stock. Ngozi sells ankara fabric in Lagos. She starts with 30 pieces, brings 10 more from her storeroom and closes with 26: 14 sold. At ₦9,000 a piece, she should have ₦126,000 in cash and transfers. If not, she knows to look that same day. Our guide to recording cash purchases works for cash sales too.

Online (your own store, Etsy, eBay, Instagram, WhatsApp), the golden rule is one stock for every channel. Deduct an item when the order comes in, not when it ships, or you will sell the same thing twice. Track parcels in transit and returns separately; a return goes back on sale only once it has been checked.

Frequently asked questions

Should I use a spreadsheet or an app for inventory?

A spreadsheet works well when one person fills it in every day. It gets fragile when several people edit it, or when you have to open a laptop for every sale. A phone app cuts the time it takes to log each movement. The best tool is the one you will actually use daily.

What is the difference between safety stock and minimum stock?

Safety stock is the buffer for surprises: a sales spike, a late delivery. Minimum stock, or the reorder point, adds normal sales during the lead time. In the example: 14 of safety stock, a reorder point of 35.

How often should a small business count inventory?

Your year-end accounts usually need a closing stock figure, so count everything at least then. Between full counts, cycle counting works better: A items weekly, B monthly, C quarterly. You catch discrepancies while you can still work out why they happened.

Should inventory be valued at cost or at selling price?

At cost. The selling price includes a margin you haven’t earned yet. For items bought at different prices, use weighted average cost or FIFO.

In short

One card per product, every movement logged the same day, a calculated reorder point and regular counts: that’s all a small business needs to manage inventory without complex software. Add ABC analysis to focus your attention and days of inventory to protect your cash. First step: pick your three best sellers and work out their reorder points today.

Sources

• Institute for Supply Management (ISM), “Mastering Safety Stock Calculations: A Step-by-Step Guide”, November 2025 (safety stock and reorder point formulas, Z = 1.65 for 95%): ism.ws.
• KPMG, “Inventory accounting: IFRS Accounting Standards vs US GAAP”, 2026 (LIFO prohibited under IAS 2, permitted under US GAAP): kpmg.com.
• Internal Revenue Service, Publication 538, Accounting Periods and Methods (inventories): irs.gov.
• H. Ford Dickie, “ABC Inventory Analysis Shoots for Dollars, not Pennies”, Factory Management and Maintenance, vol. 109, July 1951 (as cited in the literature; original not consulted).
• National Retail Federation, National Retail Security Survey 2023 (1.6% shrink in fiscal 2022, $112.1 billion; sources: external theft 36%, internal theft 29%, process and control failures 27%): nrf.com.
• Retail Dive, “After more than 3 decades, NRF won’t publish its annual shrink report this year”, 7 October 2024: retaildive.com.

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