How the calculation works
ATR starts with True Range, a single day's figure. True Range is the largest of three numbers: the day's high minus the day's low, the day's high minus yesterday's close, or yesterday's close minus today's low. Whichever of those three is biggest becomes that day's True Range. The reason for using three measures instead of just high minus low is gaps. If a stock closes at ₦50 and opens the next day at ₦55 on some piece of news, the high-minus-low range for that second day might look small even though the stock actually moved ₦5 overnight. True Range catches that by comparing the day's range to the previous close, not just to itself.
Average True Range is then a rolling average of True Range over a set number of days, usually 14. Each new day's True Range is calculated, dropped into the average, and the oldest day falls out. The result is a single figure, in the stock's own currency, that represents its recent typical daily range.
A worked example
Take a made-up stock, call it Plc X, trading on a made-up exchange, with no connection to any real listing. Over five sessions its prices move like this: day one closes at ₦120 after a high of ₦123 and a low of ₦118. Day two opens on a gap and closes at ₦126, with a high of ₦128 and a low of ₦125. Day three closes at ₦124, high ₦127, low ₦122. Day four closes at ₦130, high ₦131, low ₦123. Day five closes at ₦129, high ₦132, low ₦127.
Working through True Range for each day: day one is simply high minus low, ₦5. Day two's high-minus-low is ₦3, but high minus the prior close (₦128 minus ₦120) is ₦8, which is bigger, so day two's True Range is ₦8. Day three's high-minus-low is ₦5, and that turns out to be the largest of the three comparisons. Day four's high-minus-low is ₦8. Day five's high-minus-low is ₦5. Average those five figures and you get a True Range average of ₦6.20 for the period. A real 14-day ATR would use fourteen such figures, smoothed, but the mechanics are the same: it is simply telling you that, recently, this stock has moved by around ₦5 to ₦8 a day, averaging about ₦6.
What that figure is useful for, and what it isn't
An ATR of ₦6.20 on a stock trading near ₦125 tells you the stock has been moving close to 5% of its price in a single session. That is a statement about the stock's behaviour, not a prediction of its next move. If you are trying to judge whether a ₦3 move on a given day is ordinary or unusual for this stock, ATR gives you the context to make that judgement. It is a baseline for expectations, nothing more exotic.
Where this goes wrong is when ATR gets folded into timing decisions, such as treating a jump in ATR as confirmation that a breakout is starting, or using an ATR multiple as an automatic trigger. The flaw is that ATR has no sense of direction built in. A stock can post a high True Range reading on a day it falls sharply, a day it rises sharply, or a day it does both and closes roughly flat. The indicator answers "how much," never "which way." It is also a lagging figure by construction, an average of the past 14 sessions, so it describes a volatility regime that has already happened rather than one that is forming.
This explainer has not covered position sizing formulas built on ATR, nor lookback periods other than 14 days, nor how ATR readings compare between stocks in different sectors. Those are separate questions with their own trade-offs, and any specific figures for real Nigerian, Ghanaian or South African listings would need current price data, which this piece has deliberately avoided in favour of constructed numbers.
The honest use of ATR is as a ruler, not a signal. It tells you how wide a stock's normal range has been, which is useful background when you are assessing whether a current move looks ordinary or stretched. It does not tell you when to act on that assessment, and treating it as though it does is reading more into an average than the arithmetic supports.
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