average cost basis
Average Cost Basis is the average price you paid for shares or fund units bought at different times, used to work out your profit when you sell.
In plain English
Think of buying garri at the market over several months. In January a bag costs ₦25,000, in April it costs ₦30,000, and by August it costs ₦28,000. If someone asks you what you paid per bag, on average, you would not pick one figure and ignore the rest. You would add up everything you spent and divide by the number of bags. That average is the fair way to answer the question, and it is exactly what Average Cost Basis does for investments.
When you buy shares or fund units in bits over time, maybe ₦50,000 worth this month and another ₦80,000 worth three months later at a different price, each batch has its own cost. Selling some of those units later means you need a starting point to calculate profit. Rather than tracking every single batch and its exact price, Average Cost Basis blends all your purchases into one average price per unit, and uses that figure to work out your gain or loss when you sell.
This matters a great deal for tax. Your profit, which tax people care about, is your selling price minus your cost basis. If your cost basis is calculated wrongly, or not calculated at all, you could end up overpaying or underpaying tax, and either one causes headache later.
A Nigerian example makes it real. Say someone invests in a mutual fund through a Nigerian brokerage, buying units three separate times at different prices. When they eventually sell, the brokerage statement often shows an average cost per unit rather than three separate purchase records, because that is simpler for everyone to work with.
In the United Kingdom, this idea shows up clearly with shares held in the same company bought at different times. HMRC actually requires a version of average cost pooling for many share disposals, so understanding this concept helps you read your own tax paperwork instead of feeling lost when the numbers appear.
You buy 100 units at ₦200 each, then later 100 more units at ₦300 each. Total spent is ₦50,000 for 200 units, so your average cost basis is ₦250 per unit. If you sell 50 units at ₦350 each, your profit is calculated using ₦250 as the cost, not ₦200 or ₦300 alone.
Questions people ask
Why can't I just use the price of my most recent purchase as my cost basis?
Because that would ignore the earlier money you spent at a different price. Using only the latest price could make your profit look bigger or smaller than it truly is, which affects how much tax you owe.
Do I have to calculate Average Cost Basis myself?
Usually not. Brokerages, fund managers and investment platforms typically calculate and display it on your statements, but it helps to understand what the figure means so you can check that it looks reasonable.
Does Average Cost Basis apply to things other than shares, like property or cryptocurrency?
It can apply to any asset bought in multiple batches at different prices, including cryptocurrency. Property is usually treated differently since each property purchase tends to be tracked on its own rather than averaged.
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