Standard Deviation Indicator
StdDev is the mathematical source of volatility: the average dispersion of price around its mean — the width inside Bollinger Bands, ATR's sibling, the base ruler for every "volatility state" read.
What it is
The Standard Deviation (StdDev) indicator measures how far the last N closes disperse from their mean: σ = √(Σ(Close − MA)² ÷ N). It answers "how agitated has the market been" — high readings mean price roams far from the mean (high volatility), low readings mean price huddles near it (low volatility). It is the mathematical source of volatility measurement: Bollinger's ±2σ, annualized volatility in quant finance, implied volatility in options — all built on it. MT5's default period is 20.
Origin
Standard deviation as a statistical concept dates to the 19th century (the Gauss/Pearson lineage); technical analysis adopted it as the common language of volatility. Bollinger Bands (John Bollinger, 1980s) popularized the ±2σ channel — the StdDev indicator itself is the naked volatility reading: no channel structure, just the number. MT5's iStdDev supports multiple MA algorithms and applied prices.
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The computation (MT5 default SMA20):
Convention watch: MT5 uses the population standard deviation (divide by N); some statistical software uses the sample version (divide by N−1) — readings differ slightly. The indicator allows choosing the MA method and applied price — different combos read differently; align conventions before comparing analyses.
Worked example
An example building the "volatility state" intuition:
- Two weeks of range: closes huddle inside 100±1 → StdDev ≈ 0.5 — volatility compressed, the market quiet.
- Breakout: consecutive wide bars push price away from the old mean → StdDev surges past 3 — volatility expanding, the market agitated.
- Mature trend: price consolidates at highs → StdDev falls from its peak but stays above the range-era level — moderate volatility, trend continues.
The StdDev curve itself is the volatility cycle — compression → expansion → decay, fully visible. A low StdDev is "the calm before the storm"; a high one, "the storm in progress".
How to read it
Reading StdDev (the historical-relative method):
| Range | Common interpretation |
|---|---|
| StdDev at a historical low | Volatility compressed — a coiling range, breakout brewing (the same read as a Bollinger squeeze) |
| StdDev lifting fast | Volatility expanding — the typical start of a new trend or a major move |
| StdDev at a historical high | Extreme volatility — cut size, widen stops, or stand aside |
| StdDev falling from highs | Volatility decaying — the trend maturing or exhausting |
| A low plateau turning up | The first signal of compression ending — a breakout pre-warning |
StdDev has no direction and no OB/OS — it is a pure "state" indicator: readings must be compared against the instrument's own history (absolute values do not compare across symbols), and the direction of change matters more than the level.
Common signals & usage
Compression → expansion
A long low plateau followed by a fast lift — quantified confirmation of a breakout launch; enter with the squeeze/breakout structure.
Extreme-volatility downsizing
StdDev spiking to an extreme percentile (e.g. 95%) — re-evaluate size and stops entirely, or stand aside.
Volatility-decay tracking
StdDev falling week by week from a peak inside a trend — the move maturing; downshift trend strategies.
Calibrating other tools with StdDev
Use StdDev readings to dynamically widen envelopes or scale stop multiples — a plain-vanilla "adaptive parameter" implementation.
Limitations & common mistakes
- No direction information: StdDev measures dispersion only — rallies and crashes raise it equally; direction always comes from trend tools.
- Absolute values do not compare across symbols: a $2 StdDev means different things on a $20 and a $400 stock — use the relative form (StdDev ÷ price).
- Lags volatility shocks: a 20-period window reacts to sudden changes 2–3 days late — during events the actual volatility dwarfs the reading.
- The ATR trade-off: both measure volatility with different geometry (dispersion vs true range) — StdDev is sensitive to deviation from the mean, ATR to each bar's path; stops usually use ATR, state reads use StdDev.
- Convention traps: the MA method, applied price and population-vs-sample choices all change the reading — align before comparing.
StdDev in MT5
StdDev is a built-in MT5 oscillator (single line, sub-window). The MQL5 function for programmatic use is iStdDev:
| MQL5 function | iStdDev() |
| Default parameters | ma_period=20, ma_method=SMA |
| Algorithm | √(Σ(Close−MA)² ÷ N) (population form) |
| Buffers | 0=main buffer (StdDev value) |
| Display window | Sub-window (readings in price units) |
iStdDev exposes the MA method and applied price — different choices give different readings. Bollinger Bands compute the same family of σ internally (iBands' deviation parameter is a multiple of σ). In code, divide StdDev by price to get a percentage volatility for cross-instrument use.
Behavior across timeframes
15-minute
The intraday volatility switch: avoid low-StdDev sessions (midday), enable strategies in high-StdDev ones (open/close)
1-hour / 4-hour
Swing volatility-state monitoring; the compression→expansion confirmation period
Daily
The classic habitat: the 20-period StdDev volatility cycle is most complete on dailies
Weekly
Weekly extremes map to macro-event cycles — a background risk ruler for long-term books
Indicator combinations
Common pairings for StdDev:
- With Bollinger Bands: the band width is ±2σ visualized — the StdDev histogram adds numeric precision to squeeze/expansion reads. BOLL
- With ATR: StdDev governs the volatility state (compression/expansion), ATR governs stop placement (each bar's path) — state and execution divided. ATR
- With ADX: a low StdDev + low ADX + Bollinger squeeze all together — the classic triple signature of "the eve of a big move". ADX
FAQ
Q Is a StdDev of 2.5 high or low?
Unanswerable without history — absolute values do not compare across symbols or eras. The correct read is historical-relative: its percentile within the past year of its own readings (e.g. the 80th = elevated). For cross-symbol comparison use StdDev ÷ price.
Q StdDev and ATR both measure volatility — which one?
Different jobs: StdDev measures average dispersion from the mean (deviation-sensitive); ATR measures each bar's true path (path-sensitive, gaps included). Stops and sizing usually use ATR; volatility-state cycles (compression/expansion) usually use StdDev — together they complement.
Q Is Bollinger's σ the same calculation as the StdDev indicator?
Same family: Bollinger uses the 20-period standard deviation of closes × 2 for the channel (±2σ); the StdDev indicator outputs the same family of readings naked. Detail conventions differ (Bollinger fixes SMA and population form; MT5's StdDev allows MA choice) — with identical settings the values match.
Q Can StdDev predict the breakout direction?
No. It measures "how volatile" not "which way" — a low StdDev (compression) only says a break is brewing; direction belongs to the breakout structure. Pair it with the Bollinger squeeze (position) and the breakout bar (direction); StdDev merely confirms that volatility is expanding.
Q How do I add StdDev in MT5?
Menu: Insert → Indicators → Oscillators → Standard Deviation, or drag it from the Navigator onto a sub-window. Defaults: period 20, SMA, Close — readings are in price units (different heights across instruments are normal).
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