Record the cost of every delivery
For each delivery write: the supplier, how many, and what you paid for one pack. Not “about ₦40,000”: the exact figure on the invoice or what you transferred.
Include what it cost to get it here
Transport, loading, a market levy: if you pay it to get the goods into your shop, it is part of the cost. Spread it over the delivery. ₦20,000 transport on 40 bags adds ₦500 to each bag.
Work in the unit you sell
A ₦45,000 bag of rice sold by the kilo costs ₦45,000 ÷ 50 = ₦900 per kg. A ₦9,600 carton of 40 noodles costs ₦240 per piece. Your selling price should be set against that unit cost, not the bag price.
When you hold stock bought at different prices
There are two common ways to cost it:
- Oldest first (FIFO). What you sell is costed at the price of the oldest stock still on hand, then the next. It matches how stock actually leaves a well-kept shelf. See FIFO for small shops.
- Average. Add up what all the stock on hand cost and divide by the quantity. Simpler by hand, but it blurs price rises.
Pick one and stick to it; switching between them makes month-to-month comparisons meaningless.
Profit per item
Profit = selling price − real unit cost. If rice costs you ₦900 a kilo landed and you sell at ₦1,100, you make ₦200 a kilo, before rent and salaries. Check this for your top sellers whenever a supplier changes its price: it is how shops lose money without noticing.
Compare suppliers on the real number
The supplier with the lowest price per bag is not always the cheapest once transport, short deliveries and credit terms are counted. Keep the cost per supplier and compare like for like.