What it means
Momentum is the speed of a price move. Price rate of change measures it by comparing today's price with the price from a chosen number of periods ago, such as 12 days or 12 weeks.
A positive figure means the price is higher than it was, and a negative figure means it is lower. The indicator is usually drawn beneath the price chart as a line that moves around a zero line.
When the line is above zero and rising, upward momentum is strengthening. When it is below zero and falling, downward momentum is strengthening, and a line crossing zero can signal a change in direction.
Traders also look for extremes. An unusually high reading can suggest the price has risen too far too fast, and may be due to pause, while an unusually low reading can suggest selling has been overdone.
What counts as extreme depends on the asset, so analysts compare the reading with its own history. Another use is divergence.
If the price makes a new high but the rate of change makes a lower high, the move is losing energy, which can warn that the trend is weakening. This does not guarantee a reversal, but it is a prompt to look more carefully.
The choice of period matters. A short period, such as 5 days, reacts quickly and creates many signals, some of them false, while a long period, such as 25 days, is smoother but slower.
Many users start with 12 periods and adjust to suit the market they follow. For non-traders, the same idea works for business data.
The rate of change of sales, costs or customer numbers over a set period shows whether performance is accelerating or fading. It is simple, intuitive and easy to build in a spreadsheet.
In practice
Real-world examples.
Example
A trader sees the 12-day ROC of a stock cross above zero for the first time in two months. She treats it as a sign that buyers are taking control and starts a small position. She will add more only if the price confirms the move. Her plan limits any single trade to 1% of the account, to keep losses small if the signal fails.
Example
A commodity analyst notes that the 25-day ROC of a metal reached 20%, its highest in two years. She warns clients that the rally may be stretched and advises against buying more. The price falls 6% over the next fortnight. She reminds clients that the signal was a warning and not a certainty.
Example
A chief financial officer applies the same idea to monthly orders. The three-month rate of change in new orders turns negative, from 4% to -3%. She asks sales leaders to explain before the slowdown reaches revenue. The team finds that two large customers have delayed their orders.
Formula
Calculation
ROC = (current price - price n periods ago) / price n periods ago x 100%.
A share closed at $40 twelve days ago and closes at $46 today. ROC = ($46 - $40) / $40 x 100% = $6 / $40 x 100% = 15%. If instead the share had closed at $50 twelve days ago and now closes at $45, ROC = ($45 - $50) / $50 x 100% = -$5 / $50 x 100% = -10%. A positive reading shows upward momentum and a negative reading shows downward momentum. To use it as a rolling indicator, repeat the calculation every day with the latest close and the close from 12 days earlier. Plotting the results gives a line that moves above and below zero, which is the version drawn on charts.Case study
Seen in the real world.
Linden Capital is a fictional trading firm used here to illustrate the idea. One of its analysts followed a manufacturing share that had climbed from $30 to $42 over three months.
The 12-day ROC peaked at 18% in the first month, but by the third month it had slipped to 6%, even as the price made a new high. The analyst read this divergence as a sign that the rally was losing strength.
The illustrative firm trimmed its holding, and within six weeks the price fell back to $36. The case shows ROC as an early warning, to be combined with other evidence and not used alone.
Watch out
Common mistakes.
- Treating a high ROC as a guaranteed sell signal. Strong trends can stay stretched for a long time.
- Using a very short period and trading every wiggle. This generates many false signals and high trading costs.
- Comparing ROC across assets without context. Normal ranges differ between shares, currencies and commodities.
Questions
People also ask.
What period should I use?
Many traders begin with 12, and then test shorter or longer periods that suit the asset and their time horizon.
How is ROC different from price change?
Price change is a single difference, while ROC measures change over a fixed rolling window and plots it over time.
Is ROC the same as momentum?
They are closely related, since momentum is often the plain difference and ROC expresses it as a percentage. Using a percentage makes it easier to compare shares with different price levels.
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