Indicator
Also called Trading indicator, Chart indicator
An indicator is a calculation applied to past price or volume data and drawn on a chart as a line, histogram, arrow or zone. It summarises what the market has already done; it does not predict what comes next.
Indicators matter because traders act on them. Read one wrong, or let it set your stop without resizing the trade, and you can risk more money than you planned. The section on ATR shows how 1% turns into 2.5%.
What an indicator does with price data
An indicator takes the open, high, low, close or volume of recent bars, runs a fixed formula over them and plots the result. Nothing else goes in. It does not see news, interest-rate decisions or the orders waiting in the market.
The period is the number of bars the formula looks back over.
An indicator is drawn in one of two places. An overlay sits on the price chart and shares its scale, like a moving average. A sub-window indicator sits below the chart on its own scale, like an oscillator, a line that swings between set limits such as 0 to 100. The drawing below shows both built from the same price series.
The five indicator families and the question each answers
Most indicators belong to one of five families. Knowing the family tells you what the tool can and cannot say.
| Family | Question it answers | Common examples | Drawn |
|---|---|---|---|
| Trend | Which way is price drifting? | EMA, an exponential moving average that weights recent closes more | On price |
| Momentum | How fast is the move? | RSI, a 0 to 100 reading of recent gains against losses; CCI, how far price sits from its own average | Sub-window |
| Volatility | How far does price travel per bar? | ATR, the average true range of recent bars; true range is a bar's high-to-low distance, including any gap from the prior close | Sub-window |
| Volume | How much activity is behind the move? | Volume bars, which in spot forex usually count price updates rather than traded size | Sub-window |
| Levels | Where might price react? | CPR, the central pivot range: three levels from the prior day's high, low and close | On price |
Two indicators from the same family largely repeat the same information. Two momentum oscillators built from the same closes will turn together, for example. They agree because they share a formula idea, not because the signal is stronger. Pick one per question.
The three ways an indicator gives a signal: crossover, level, divergence
Almost every indicator signal is one of three events. Learn to name which one you are looking at before you act on it.
- Crossover. Two lines cross, or price crosses an indicator line. If a faster line crosses above a slower one on a closed bar, consider only buy setups until it crosses back.
- Level. An oscillator reaches a fixed line, such as 70 or 30 on RSI. If RSI drops to 30, wait for it to climb back above 30 before looking for a buy; the touch alone is not the cue. In a strong trend RSI can stay above 70 for many bars; while price keeps making higher highs, read it as strength, not a sell.
- Divergence. Price and the oscillator disagree. If price makes a higher high but the oscillator makes a lower high, stop adding to buys and tighten your plan on open ones; do not sell on divergence alone.
The chart below shows two of these on one RSI panel. RSI dips below 30 at the price low and climbs back above it on the next bar, which is the buy cue. Later, price makes a higher high while RSI makes a lower high.
Leading vs lagging: why every indicator trails price
Indicators are often sorted into leading and lagging, but any indicator built from past bars trails price. A simple moving average runs roughly half its period behind, so a 20-period average mostly reflects where price was about 10 bars ago. Oscillators often called leading turn sooner because they measure the speed of a move. They still use only bars that have already printed, so they can show that a move is slowing, not that it will reverse.
The decision rule: if you need early entries, use a shorter period and accept more false turns. If you need fewer false signals, use a longer period and accept later entries.
Applied price and timeframe: two settings that change the reading
Beyond reading an indicator, you can change how it is built: the price it is applied to (most often the close), fixed levels for oscillators, and colours. Switch a moving average from the close to the high and it runs along the tops of the bars, above the close-based line; switch it to the low and it runs along the bottoms, below it.
An indicator belongs to one chart and one timeframe, so the same setting covers a different stretch of time on each chart: a 20-period on the 1-hour chart covers 20 hours; on the daily chart it covers 20 trading days.
How an ATR reading changes your stop and lot size
An indicator affects a trade most directly when its number feeds your risk maths. The figures here are an illustrative example.
You have a $10,000 account and risk 1% per trade. ATR on your EUR/USD chart reads 0.0020, which is 20 pips. Your rule is a stop of 2 × ATR. One standard lot on a USD-quoted pair is worth $10 per pip.
Now suppose the market gets busier and ATR reads 50 pips. The stop becomes 50 × 2 = 100 pips, and the size becomes $100 ÷ (100 × $10) = 0.10 lots. The risk is still $100, with a wider stop and a smaller position.
A trader who ignores the reading and keeps 0.25 lots with the 100-pip stop risks 100 × $10 × 0.25 = $250, which is 2.5% of the account.
Checks before you trust an indicator reading
- Wait for the bar to close. The value on the bar still forming moves with every tick. A cross or arrow that appears mid-bar can vanish by the close, as the drawing under this list shows.
- Read the settings, not only the name. Two charts both labelled RSI can use 9 and 14 periods; check the number in the label before you compare readings.
- Scroll back and look at the losers. Find the places where the signal failed, not only the clean ones.
- Ask whether old signals move. Some custom indicators redraw past arrows once new bars arrive, which makes history look better than live trading was.
- Apply the removal rule. If a reading would not change your entry, stop or size, take the indicator off.
FAQ
How many indicators should I put on one chart?
One per question from the family table (trend, momentum, volatility) is usually enough; a second from the same family adds clutter, not confirmation. Then use the phone-screen test. If you cannot see the candles clearly on a phone screen, you have too many.
Can an indicator place trades for me?
No. An indicator only draws and, at most, sends an alert. Opening and closing orders automatically is done by an automated trading program (a trading robot).
Why does my indicator show different values on another broker's chart?
The formula is the same, but the bars are not. Each broker has its own price feed, and its bars can open at different times, so the highs, lows and closes going into the calculation differ slightly.