# What Is Relative Strength? How to Compare a Stock to the Market

Source: https://cluenex.com/learn/technical-analysis/relative-strength/
Publisher: Cluenex (https://cluenex.com)
Updated: 2026-10-15

## Short answer

Relative strength (RS) compares a stock's performance to a benchmark, usually the S&P 500. Divide the stock's price by the index level: if the line rises, the stock is beating the market. It describes the past and is not a guarantee of future returns.

## Key takeaways

- Relative strength is a ratio: stock price divided by benchmark level. A rising line means the stock is beating the benchmark over that period.
- Relative strength is not RSI. RSI measures how fast one price moved, while RS compares two prices.
- Academic research on momentum finds that past winners have tended to keep beating past losers over 3 to 12 months, but the effect is uneven and can reverse sharply.
- An RS line says nothing about whether a stock is cheap or expensive, so pair it with valuation and business quality checks.
- Treat RS as a way to build a watchlist, not as a standalone buy or sell trigger.

## What is relative strength?

Relative strength is a comparison of how one stock has performed against a benchmark, most often the S&P 500. It answers a simple question: is this stock beating the market or trailing it?

A stock can rise 8% and still be a laggard if the market rose 12% over the same period. Relative strength makes that visible.

This idea is popular with investors who follow momentum, meaning the tendency of recent winners to keep winning for a while. William O'Neil's book *How to Make Money in Stocks* helped popularize RS rankings among individual investors.

## How do you calculate relative strength?

Divide the stock's price by the benchmark's level, then plot that ratio over time. Many charting tools multiply by 100 to make the numbers easier to read, but the scaling does not change the shape of the line.

Worked example with made-up round numbers:

| Date | Stock price | S&P 500 | RS (price ÷ index × 100) |
|---|---|---|---|
| Start | $100 | 5,000 | 2.000 |
| Later, stock beats market | $108 | 5,200 | 2.077 |
| Later, stock trails market | $102 | 5,200 | 1.962 |

In the second row the stock gained 8% and the index gained 4%, so RS rose from 2.000 to 2.077. In the third row the stock gained only 2% against the index's 4%, so RS fell to 1.962.

The RS number itself means nothing. Only the direction and slope of the line matter.

## How do you read an RS line?

A rising RS line means the stock is outperforming the benchmark. A falling line means it is lagging. A flat line means it is moving with the market.

Three readings come up most often:

- **Rising line:** the stock has been beating the market over the window you are viewing.
- **RS at a multi-month high:** the stock is at its strongest relative to the market in that period.
- **Divergence:** the stock's price makes a new high but the RS line does not. That means the stock is rising mostly because the whole market is rising, not because it is leading.

These are descriptions of what already happened. None of them is a forecast on its own.

## Is relative strength the same as RSI?

No. The Relative Strength Index (RSI) is a momentum oscillator that looks at one stock's own recent gains and losses and scales them from 0 to 100. Relative strength compares two prices, the stock and a benchmark.

The names are similar, which causes confusion. A stock can have a high RSI while its RS line is falling, or the reverse. See [What is RSI](/learn/technical-analysis/rsi-explained/) for the oscillator.

## Does relative strength predict future returns?

To a degree, over medium horizons. Academic studies of momentum, starting with Jegadeesh and Titman (1993), found that US stocks with the best returns over the past 3 to 12 months tended to outperform the worst performers over the following 3 to 12 months.

That finding is about averages across many stocks. It does not say any single stock with a rising RS line will keep winning.

Momentum has also had severe reversals. After market crashes, past losers can bounce hard and past winners can fall behind quickly, which hurts momentum portfolios.

## What are the limits of relative strength?

RS describes the past, ignores price, and is sensitive to the window and benchmark you choose. Those are the main reasons it fails.

Common problems:

- **It ignores valuation.** A leader can be leading because its price has run far ahead of its profits. Strong RS plus a stretched price is a risk, not a comfort. See [P/E ratio explained](/learn/technical-analysis/pe-ratio-valuation/).
- **Choice of benchmark.** A technology stock measured against the S&P 500 may look strong simply because technology is leading. Compare it with its own sector too.
- **Choice of window.** A stock can look strong over 3 months and weak over 12. Check more than one window.
- **Crowding and reversals.** When many investors chase the same leaders, a shift in sentiment can send them down together. See [sector rotation](/learn/markets/sector-rotation-explained/).
- **Falling markets.** In a decline, a stock that falls less than the index still shows a rising RS line while losing you money.
- **Single events.** One earnings jump or takeover headline can lift an RS line without any lasting change in the business.

One claim common in older guides is that RS breakouts win 65% to 75% of the time. No credible published test supports a figure like that for individual traders, so treat any precise win rate you see attached to RS with suspicion.

## How can RS be used alongside other checks?

Use RS to narrow a list, then ask whether the business and the price justify a closer look. RS answers "what is the market rewarding?" It does not answer "is this worth owning at this price?"

A sensible sequence:

1. Scan for stocks whose RS line has been rising over several months.
2. Check that the strength comes from real results such as growing revenue and profit, not just a price jump.
3. Look at valuation against the stock's industry. Cluenex has a free [sector benchmarks page](/learn/data/sector-benchmarks/) with typical margins and P/E ratios by sector.
4. Decide how much you could lose and size the position to match. See [position sizing](/learn/portfolio-management/position-sizing/).

Cluenex charts include common technical indicators, but Cluenex treats chart patterns as context rather than buy or sell signals, because its own tests found no reliable directional edge in them. The same caution applies to RS lines.

## What this means for you

If you have a regular job and a brokerage account, treat relative strength as a filter for attention, not a trigger for trades.

- Compare any stock you hold with the S&P 500 and with its sector over 3, 6 and 12 months. A holding that has lagged on all three deserves a written reason to stay.
- Never buy a stock only because its RS line is rising. Check profit growth and valuation first.
- Avoid rules that promise a fixed win rate. Real results vary with the market period.
- If you own a broad index fund, you already hold the leaders in proportion to their size. Chasing RS adds trading costs and taxes that may not pay off.
- Review RS on a schedule, such as quarterly, rather than checking it daily.

## Questions people ask

### What is a good relative strength number?

There is no good absolute number, because the ratio depends on the stock's price and the index level. What matters is whether the line is rising or falling over your chosen period, and how it compares with other stocks.

### How is relative strength different from momentum?

Momentum usually measures a stock's own past return, while relative strength measures that return against a benchmark. The two are closely related, and many momentum strategies rank stocks by their return relative to the market.

### Can a stock have strong relative strength in a falling market?

Yes. If the stock falls 5% while the S&P 500 falls 10%, its RS line rises even though you lose money. Relative strength shows how a stock fared against the market, not whether it made a profit.

### What benchmark should I use for relative strength?

The S&P 500 is the usual choice for large US stocks. For a more useful comparison, also measure against the stock's sector or industry group, since sector trends can drive most of the difference.

### How long should I look back when measuring relative strength?

Academic momentum studies typically use 3 to 12 months. Checking several windows, such as 3, 6 and 12 months, protects you from judging a stock on one lucky or unlucky stretch.

## Sources

- [Returns to Buying Winners and Selling Losers: Implications for Stock Market Efficiency (Jegadeesh and Titman, 1993)](https://www.jstor.org/stable/2328882)
- [Momentum Crashes (Daniel and Moskowitz)](https://www.nber.org/papers/w20439)
- [S&P 500 index overview](https://www.spglobal.com/spdji/en/indices/equity/sp-500/)
- [Relative strength index (RSI)](https://www.investor.gov/introduction-investing/investing-basics/glossary)

Cite as: Cluenex. "What Is Relative Strength? How to Compare a Stock to the Market." Cluenex Learn, updated Oct 15, 2026. https://cluenex.com/learn/technical-analysis/relative-strength/