Module 4 · Lesson 5 of 12 · Volume and indicators · About 5 minutes
RSI and Stochastic Oscillators: What Overbought Really Means
On this page
Before you read: Moving Averages in Depth: SMA, EMA, Lag and Crossovers
What you will learn
- How the relative strength index (RSI) and the stochastic oscillator are built from price.
- What overbought and oversold readings describe, and why they can last a long time.
- What a divergence between price and an oscillator is, and why it is not a reversal signal on its own.
What is an oscillator?
If a line is forced to stay between 0 and 100, what does it lose and what does it gain?
An oscillator turns price movement into a line that moves within a fixed band, usually 0 to 100. That makes readings comparable over time and across markets. It also hides the size of moves: a reading of 70 looks the same whether price rose 1% or 10%.
How is RSI calculated?
How could you compare the strength of up days with the strength of down days?
RSI compares the average size of recent gains with the average size of recent losses, usually over 14 bars:
- For each bar, record the gain (if the close rose) or the loss (if it fell).
- Average the gains and average the losses over the window, using a smoothing method introduced by its creator, J. Welles Wilder.
- Compute RS = average gain ÷ average loss, then RSI = 100 − 100 ÷ (1 + RS).
If gains and losses are equal, RS is 1 and RSI is 50. If there are only gains, RSI approaches 100. If there are only losses, it approaches 0. RSI measures how one-sided recent closes have been, not how far price has gone.
How is the stochastic oscillator calculated?
Where did today’s close land inside the recent high-low range?
The stochastic oscillator measures where the latest close sits within the high-low range of the last N bars, often 14:
%K = 100 × (close − lowest low) ÷ (highest high − lowest low).
A close at the top of the range gives 100; a close at the bottom gives 0. A smoothed version, %D, is a short moving average of %K, often 3 bars. Many platforms show a “slow” stochastic that adds one more round of smoothing. This is closely related to the close location idea from the candlestick lessons, measured over many bars instead of one.
Try it on a chart
- RSI and Stochastic are added below the price. Compare how each moves over the same bars.
- Open each one's settings and read its length.
Charts and quotes are TradingView's data, not ours, and may be delayed.
What do overbought and oversold mean?
If a market keeps closing near its highs for weeks, is that a warning or a description?
Readings above 70 on RSI, or above 80 on a stochastic, are often labeled overbought. Readings below 30 or 20 are labeled oversold. These are conventions, and the words are misleading. “Overbought” only means recent closes have been strongly one-sided. It does not mean price is too high or due to fall.
In a strong trend, an oscillator can stay in overbought or oversold territory for a long time while price keeps moving the same way. In a range, readings swing between the extremes more often.
What is a divergence?
If price makes a new high but the oscillator does not, what has changed?
A divergence is a disagreement between price and an indicator. A bearish divergence is price making a higher high while the oscillator makes a lower high. A bullish divergence is price making a lower low while the oscillator makes a higher low. It shows that the latest push came with less one-sided closing than the last one.
Divergences are easy to find with hindsight and can persist through several more highs or lows. They describe a change in the character of the move, not its end. The delta divergence idea in the order flow lessons applies the same logic to volume.
Oscillator diagram
Illustrative diagram constructed for teaching. Not real market data.
The diagram shows a fictional price path above an RSI panel with lines at 70 and 30. RSI stays above 70 through much of the rise, then makes a lower high while price makes a higher high. It is constructed for teaching and is not real market data.
What this does not tell you about oscillators
- Overbought and oversold are labels for recent behavior, not forecasts.
- The thresholds (70/30, 80/20) and lengths (14) are conventions. Changing them changes every reading.
- A divergence can last a long time and may never be followed by a reversal.
- Nothing here suggests buying, selling or holding at any reading.
Method in Practice: the same reading, two different plans
Fictional example. John, Harbor Index futures, the prices, times, costs and results are all invented for teaching. This shows how a written plan can be built and tested. It is not a recommendation, and nothing here says how often this idea works.
Try it on a real chart. Look at the chart in this lesson, then test this idea yourself on past sessions with bar replay. Keep your own count, including the days with no trade.
The idea. "Oversold" is a label for recent behavior, not a forecast (this lesson). An RSI under 30 means something different in a range than in a trend. John only uses it inside his balance plan from Auction Market Theory Basics: Balance, Value, Rotation, at the bottom edge of a range. When the market is trending, the same reading switches nothing on.
John's plan
- Setup
- five sessions rotating between 98.00 and 101.00 (balance, as in Auction Market Theory Basics: Balance, Value, Rotation)
- Enter if
- price trades below 98.20 with RSI(14) under 30 on 30-minute bars, then a period closes back above 98.20. Buy.
- Wrong if
- a 30-minute period closes below 97.90, outside the range
- Manage
- take half at 99.50 (the middle), the rest at 100.40 or by 14:30
- Risk
- $150 maximum, costs included
Three outcomes
-
Worked: oversold at the range low, and the range held → +$263
-
Failed: oversold, then the range broke and RSI stayed under 30 → −$116, inside the limit
-
No trade: RSI was 22, but the market had already left the range, so the plan was off → $0
Show the full replays
| Item | Plan |
|---|---|
| Context | Balance: five sessions inside 98.00–101.00. Plan off if the prior session closed outside the range |
| Entry condition | Price trades below 98.20 while RSI(14, 30-minute closes) is under 30, then a period closes back above 98.20. Buy 2 at market after that close |
| Wrong if | A 30-minute period closes below 97.90. Exit at market after that close |
| Management | Take profit on half at 99.50 (limit) and move the exit for the rest to the entry price (stop). Rest at 100.40 (limit). Time limit 14:30 CT |
| Risk cap and size | $150. Exiting just under 97.90 is planned to cost about $55 per contract, so 2 contracts |
| Not trading if | Scheduled major release within the hour, or no setup by 12:00 CT |
Replay A: worked
| Time (CT) | What happened | John |
|---|---|---|
| 08:30–09:00 | Falls to 98.05. RSI 27 | Watching |
| 09:00–09:30 | Closes 98.31 | Condition met: buys 2 at market, filled 98.36 |
| 09:30–11:40 | Rotates up, trades 99.50 at 11:40 | Sells 1 at 99.50 (limit). Exit for the other moves to 98.36 |
| 11:40–14:30 | High 100.15, never 100.40, never back to 98.36 | At 14:30 sells the last 1 at market: price 100.00, filled 99.95 |
Result after costs: +1.14 points = +$114, +1.59 points = +$159, commissions −$10. Net +$263. Journal: "Oversold at the edge of a range that held. The time limit closed the rest."
Replay B: failed
| Time (CT) | What happened | John |
|---|---|---|
| 08:30–09:00 | Falls to 98.02. RSI 26 | Watching |
| 09:00–09:30 | Closes 98.28 | Buys 2 at market, filled 98.33 |
| 09:30–10:00 | Breaks down, closes 97.85 | Wrong-if met: sells 2 at market, filled 97.80 |
| 10:00–15:00 | Trends to 96.90. RSI stays under 30 for four hours | Done for the idea |
Result after costs: 2 × −0.53 point = −$106, commissions −$10. Net −$116. Journal: "The range broke. Oversold got more oversold. The wrong-if line was the only part of the plan that mattered."
Replay C: no trade
| Time (CT) | What happened | John |
|---|---|---|
| Pre-open | Yesterday closed at 97.40, below the range | Plan off: no balance today |
| 08:30–12:00 | RSI 22 at 09:30, and price keeps falling to 96.60 | Watches only |
Result: $0. Journal: "The lowest RSI of the month, and the plan was off. In a trend it's just a description."
Test it yourself
- Write which context each reading belongs to, and what the plan does in the other contexts.
- Replay every RSI-under-30 reading. Split the results by "in balance" and "trending".
- Change 30 to 25 and 14 to 10. If the results flip, the rule depends on the setting (Overfitting and Repainting: When Indicator Results Look Too Good).
Where it breaks
- In a trend, "oversold" can stay oversold for hours (the failed replay).
- 70/30 and 14 are conventions, not laws.
- A range is only clear after it's drawn.
Calculators: position sizerisk/rewardexpectancy
Reflection question: When your plan says "oversold", does it also say in which kind of market?
Check yourself
- Average gains and average losses over 14 bars are equal. What is RSI? Hint: RS is 1.
- The 14-bar range runs from $40 to $50 and the close is $48. What is %K? Hint: (48 − 40) ÷ (50 − 40).
- Why can RSI stay above 70 for weeks? Hint: what does a strong trend do to recent closes?
Reflect on your own process
- Where in your written plan do the words overbought or oversold appear, and what exactly do you mean by them?
- Which oscillator thresholds and lengths does your checklist use, and have you recorded why you chose them?
- When you journal a divergence, do you also record the cases that did not reverse?
- When your plan says "oversold", does it also say in which kind of market?