Relative Strength Comparison: How to Measure a Stock Against the Market
Relative strength comparison measures how a stock is performing compared to a benchmark, like the S&P 500, over the same period. If a stock is rising faster than the benchmark (or falling slower during a downturn), it has positive relative strength. If it’s lagging the benchmark, it has negative relative strength.
This is a different concept from the Relative Strength Index (RSI), which measures a stock’s momentum against its own recent price history. Relative strength comparison instead measures one thing against another: usually a stock against an index, or a stock against its sector.
Why Compare a Stock to the Market at All?
A stock can go up 10% in a year and still be a disappointing investment if the overall market went up 25% during that same stretch. On the flip side, a stock that only fell 5% while the market dropped 20% actually held up quite well by comparison. Looking at price alone, without context, can be misleading.
In practice, many traders and analysts use relative strength as an early screen: strong stocks in a rising market often keep leading, and weak stocks often keep lagging, at least for a while.
How to Calculate Relative Strength
The most common simple method is the relative strength ratio:
Relative Strength Ratio = Stock Price ÷ Benchmark (Index) Price
You then plot this ratio as a line on a chart over time.
- If the line is rising, the stock is outperforming the benchmark.
- If the line is falling, the stock is underperforming the benchmark.
- If the line is flat, the stock is moving roughly in line with the benchmark.
A Simple Example
Say a stock trades at $50 and the S&P 500 index sits at 5,000. The ratio is 50 ÷ 5,000 = 0.01.
Three months later, the stock trades at $60 (up 20%) while the index sits at 5,200 (up 4%). The new ratio is 60 ÷ 5,200 = 0.0115.
The ratio rose, confirming the stock outperformed the index over that period, by a wider margin than the raw price change alone might suggest at first glance.
Percentage Comparison Method
An easier version for beginners: just compare percentage returns over the same period.
- Calculate the stock’s percentage change over a set period (say, three months).
- Calculate the benchmark’s percentage change over the same period.
- Subtract the benchmark’s return from the stock’s return.
If the result is positive, the stock outperformed. If negative, it underperformed.
What Counts as a Good Benchmark?
- Broad market index: the S&P 500 or a similar total-market index, for comparing against the overall market.
- Sector index or ETF: comparing a stock to peers in its own industry (a bank stock against a financial sector index, for example) often gives a more useful, apples-to-apples read than comparing it to the broad market.
- Specific competitor: comparing two similar companies directly can highlight which one the market currently favors.
Reading Relative Strength Trends
| Relative Strength Line | What It Suggests |
|---|---|
| Rising during a market uptrend | Stock is a market leader, gaining faster than peers |
| Rising during a market downtrend | Stock is falling less than the market, showing relative resilience |
| Falling during a market uptrend | Stock is lagging, may be losing favor with investors |
| Falling during a market downtrend | Stock is underperforming even the weak broader market |
How Traders Use Relative Strength Comparison
- Stock screening. Some traders scan for stocks showing strong relative strength as a starting shortlist before doing further research.
- Sector rotation. Comparing sector indexes against the broad market can highlight which parts of the market are currently in favor.
- Confirming a breakout. A stock breaking out to new highs while also showing rising relative strength is generally viewed as a more convincing signal than a breakout with flat or falling relative strength.
- Risk management. A stock that starts underperforming its benchmark, even while still in an uptrend, can be an early warning sign worth watching more closely.
Common Mistakes Beginners Make
- Confusing relative strength comparison with the RSI indicator. They share a similar name but measure completely different things. RSI looks inward at a stock’s own price momentum; relative strength comparison looks outward at how a stock performs versus something else.
- Using the wrong benchmark. Comparing a small biotech stock to the S&P 500 tells you less than comparing it to a biotech sector index or its direct peers.
- Reading too much into short time windows. A single week of outperformance doesn’t say much. Looking at relative strength trends over several months gives a more reliable read.
- Ignoring the direction of the overall market. Relative strength is about comparison, not absolute performance. A stock can show strong relative strength while still losing money in absolute terms, if the market is falling even faster.
Key Takeaways
- Relative strength comparison measures a stock’s performance against a benchmark, such as a market index, sector index, or competitor.
- A rising relative strength ratio or line means the stock is outperforming the benchmark; a falling one means it’s underperforming.
- It’s calculated by dividing (or comparing percentage returns of) the stock’s price against the benchmark’s price over the same period.
- It’s a different tool from the Relative Strength Index (RSI), despite the similar name.
FAQ
What’s the difference between relative strength and the RSI indicator?
Relative strength comparison measures a stock’s performance against a benchmark like an index. The RSI (Relative Strength Index) measures a stock’s own momentum based on its recent gains and losses. They’re unrelated despite sharing similar wording.
Which benchmark should beginners use first?
A broad market index like the S&P 500 is a reasonable starting point, since it reflects the overall market. From there, comparing a stock to its sector index often gives a more precise read.
How often should I check relative strength?
Checking weekly or monthly is common for longer-term investing decisions. Day traders sometimes check intraday relative strength against a sector ETF to spot leaders and laggards during the trading session.
Can a stock have strong relative strength and still lose money?
Yes. If a stock falls 5% while the benchmark falls 15%, the stock shows strong relative strength (it held up better) even though it still lost value in absolute terms.
Is relative strength comparison useful for long-term investors, or just traders?
Both. Long-term investors often use it to identify sector leaders or confirm that a holding is keeping pace with, or beating, the broader market over time, not just short-term traders looking for momentum.
