What is RSI and When Should You Buy a Stock?
RSI — the Relative Strength Index — is one of the most widely used indicators in stock trading. It tells you whether a stock has been beaten down too far or run up too fast. Here's how to read it and use it.
The Simple Explanation
Every stock moves up and down. Sometimes it moves too much in one direction — sellers panic and push it lower than the fundamentals justify, or buyers pile in and push it higher than makes sense.
RSI measures the speed and size of these moves on a scale from 0 to 100. The idea is simple: when a stock gets pushed to an extreme, it tends to snap back.
Think of RSI like a rubber band. The further you stretch it in one direction, the more likely it is to snap back.
How to Read the RSI Scale
When RSI drops below 35, the stock is considered oversold. This means sellers have been dominant and the stock may be priced below its fair value. Historically, oversold conditions have preceded recoveries more often than not.
When RSI rises above 65, the stock is overbought. Buyers have pushed the price up fast, and a pullback becomes more likely.
The middle range (35–65) is neutral territory — no strong signal in either direction.
How RSI is Calculated
RSI looks at the last 14 trading days by default. It compares the average size of up days vs. down days:
The formula:
RSI = 100 - (100 / (1 + (avg gain / avg loss)))
You don't need to calculate this manually — any charting platform shows RSI automatically.
The 14-day period is the standard, but some traders use shorter periods (7 days) for more sensitive signals or longer periods (21 days) for smoother readings.
Real Examples — What RSI Looks Like in Practice
Here are some recent RSI readings that illustrate extreme conditions:
| Stock | RSI | Signal | What it means |
|---|---|---|---|
| MSFT (Microsoft) | 17 | Strong buy signal | Down ~30% from peak, AI spending fears |
| GOLD (Barrick Gold) | 19 | Strong buy signal | Miners lagging physical gold price |
| WPM (Wheaton Metals) | 44 | Neutral — watch | No clear entry point yet |
MSFT at RSI 17 was one of the most extreme oversold readings for a major company in recent years. Historically, readings that low have been followed by significant recoveries — not immediately, but over weeks and months.
RSI is a Timing Tool, Not a Prediction
This is important. RSI doesn't tell you if a stock will go up — it tells you when conditions are historically favorable for a recovery.
A stock can stay oversold for a long time. A fundamentally broken company can have RSI 10 and keep falling. RSI works best when combined with a basic check on the underlying business: is this a good company that got beaten down by fear, or a bad company that deserves to be down?
Microsoft at RSI 17 is a different situation than a penny stock at RSI 17.
Why Most Investors Miss RSI Signals
Here's the frustrating reality: even if you know about RSI, you'll miss most signals unless you're watching constantly.
Stocks hit oversold conditions and bounce fast. MSFT dropped to RSI 17 on a Tuesday and started recovering by Friday. If you only check your portfolio on weekends, you missed it.
Most people check their stocks when they're excited — when prices are going up and everyone is talking about them. That's exactly the wrong time. You want to know about stocks when they're quiet, beaten down, and nobody's paying attention.
How to Get RSI Alerts Automatically
You have a few options:
DIY: Set up RSI indicators on TradingView, Thinkorswim, or any charting platform and check them manually. Free, but requires you to remember to look.
Brokerage alerts: Most brokerages let you set price alerts, but few support RSI-based alerts. You'd need to calculate RSI thresholds yourself and set price alerts as proxies.
Dedicated alert service: Built Wealth Alerts monitors RSI on your watchlist every hour during market hours and sends you a Telegram message the moment a signal fires. You don't have to watch anything — your phone buzzes when it's time to look.
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See plans starting at $29/month →Common RSI Mistakes to Avoid
1. Treating RSI as a guarantee
RSI below 30 doesn't mean the stock will definitely bounce. It means conditions are historically favorable. Always combine RSI with basic fundamental research.
2. Using RSI on the wrong timeframe
Daily RSI (14-day period) is the standard for swing traders and investors. If you're looking at 5-minute charts, the RSI will be much noisier. Match your RSI timeframe to your investment horizon.
3. Ignoring the trend
In a strong downtrend, RSI can stay oversold for weeks. RSI works best in ranging markets or at the tail end of corrections. Be more cautious with RSI signals during sustained bear markets.
4. Acting on RSI alone
RSI is one signal. Combine it with volume (is there unusual selling pressure?), news (is there a real reason for the drop?), and basic fundamentals (is this company healthy?).