Parabolic SAR

Parabolic SAR — "stop and reverse" — is a trailing stop system published by J. Welles Wilder in 1978 and drawn as dots that sit below price while the system reads the market as rising and above it while falling. Each bar the level moves toward price by a fraction of the distance between them: `SAR_next = SAR + AF x (EP - SAR)`, where EP is the most extreme price since the current direction began and AF is an acceleration factor that starts at a step value (conventionally 0.02), rises by that step at each new extreme, and is capped (conventionally at 0.20). When price reaches the level the system flips: the position closes and an opposite one opens, the SAR resets to the prior extreme and AF to its starting value.

Two properties follow and explain most of what catalogued versions do. The indicator is always in one of two states — there is no neutral reading — so the literal implementation is permanently in the market. And the gap between price and the dot depends on time in trend and on new extremes, not on volatility: a move that keeps running without a new high or low is trailed by a stop that tightens anyway, whether the market has calmed or turned wilder. That makes Parabolic SAR good at giving back little at the end of a directional run and poor at tolerating a range.

## Parameters and what they control

Two numbers define the classic version: the step and the maximum acceleration. The step sets how aggressively the stop closes in as new extremes appear — a small step trails loosely and flips rarely, a large one hugs price and flips often. The maximum caps how tight the trail can ever become. Many implementations also expose the initial AF separately. Because the step controls flip frequency, it changes the trade count and cost profile, not only sensitivity.

## Main variants

- **Stop-and-reverse** — every flip closes one position and opens the opposite, as Wilder specified. - **Exit-only** — entries come from elsewhere; the dots are purely a trailing stop. - **Bias filter** — the side of the dot sets permitted direction, another tool triggers. - **Trend confluence** — a moving-average stack, ADX/DMI or another trailing system must agree before a flip is acted on. - **Momentum confirmation** — MACD, RSI or stochastic validates or vetoes the flip. - **Multi-timeframe** — a higher-timeframe SAR gives direction, a lower one the entry. - **Restricted flips** — only the first dot after a reversal is tradable, or several must print first. - **Alternative input series** — Heikin Ashi candles or Renko bricks instead of standard bars. - **Adaptive step** — acceleration tied to a volatility or trend-strength measure instead of fixed.

## What typically differentiates implementations

Less the parameters than the role. Whether the flip is an entry, an exit or only a filter changes the system completely, as does whether a flat state is allowed — the indicator never offers one, so any version that stands aside gets it from its filters. **Execution timing** matters as much: an intrabar touch, a confirmed close beyond the dot and a next-bar open fill are three different strategies. **Stop handling** divides them again, because the dot moves every bar: a stop at the dot ratchets, while one beyond structure leaves the SAR signalling but not protecting. That decides **position sizing**, since risk measured to a level that starts far away and then closes in is not constant. And the **filter stack** sets where the version may trade at all.

## Common mistakes

Trading every flip in a range is the recurring one: with no neutral state the system reverses at each crossing, paying the spread both ways. Treating the dots as support or resistance to buy against inverts their meaning — they are invalidation levels, not targets. A subtler error is testing a touch of a dot computed from the same bar's high or low — a value known only at the close — which produces fills at prices that were never available. Renko or Heikin Ashi output fails for a different reason: those series are derived and never traded. Ignoring costs is especially damaging because the step controls frequency, and tuning it until an isolated peak appears fits the sample rather than the market.

## How to evaluate and backtest a version

Pin the definition down first — step, maximum, initial AF, confirmation rule, execution timing, whether reversals are taken or only exits, and whether a flat state exists — then reproduce the dots independently, since platforms differ in how they seed and reset the calculation. Benchmark against the plain always-in stop-and-reverse on the same data: every filter added should visibly earn its complexity. Test the entry and exit roles separately, holding one fixed while swapping the other. Examine the surface across step and maximum, preferring a broad plateau to a spike. Segment by regime and by year, apply realistic costs at each flip, and check how concentrated the outcome is in a few trades. Then validate out of sample or with walk-forward, on more than one instrument, reading long and short separately.

The three decoded versions linked from this page differ along exactly these axes: whether the flip generates the trade or only closes it, what supplies direction, and what the rules do without a trend.

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Frequently asked questions

What are the standard Parabolic SAR settings?

Wilder's configuration is a step of 0.02 with a maximum acceleration of 0.20, and it is a starting point rather than a rule. The step controls how quickly the stop closes in as new extremes print, so it governs how much of a pullback the version tolerates and, consequently, how many trades it takes; the maximum caps how tight the trail can become during an extended move. Some implementations also expose the initial acceleration separately, and leaving it at a different value from the step changes early behaviour after every flip. Because trade count and cost move together here, prefer a setting inside a broad region of similar behaviour over an isolated optimum found by sweeping one number.

Does Parabolic SAR repaint?

The value on a closed bar does not change, but the level for the bar currently forming depends on that bar's own high or low, so it can move, and price can touch it and pull back before the bar closes. A version that acts on an intrabar touch is therefore not the same system as one that waits for a confirmed close, and only the second is straightforward to reproduce in a backtest. The same issue appears in code that computes a bar's SAR using information from that bar and then tests it against prices earlier in the bar. Multi-timeframe versions add a second source of it, since a higher-timeframe dot read without correct offsetting is a value that was not yet available at that moment.

Why does Parabolic SAR struggle in sideways markets?

Because it has no flat state. The indicator is always labelled up or down, so a version that trades every flip is always positioned, and in a range price repeatedly reaches the dot without following through, reversing the position each time and paying costs on both sides. Widening the step reduces how often that happens but also delays the exit when a genuine trend ends, which is the trade-off the parameter actually controls. This is why most catalogued versions either add a trend-strength or volatility condition that allows the system to stand aside, or use the dots only as an exit while the entry comes from elsewhere. When assessing a version, segment its results by regime: if the gains come entirely from a few trending stretches, the range behaviour is the part that needs work.

Is a Parabolic SAR flip an entry signal or an exit signal?

Mechanically it is a stop being hit, and the reversal is a design choice Wilder attached to it rather than something the calculation establishes about the market. That distinction matters when reading versions: using the flip as an exit for a position opened on other criteria is a different claim from using it as an entry, and the two are worth testing separately. In practice many catalogued implementations keep the exit role and replace the entry, because the acceleration rule is built to follow a move that already exists, not to identify where one begins. A useful check is to hold the entry logic fixed and swap the exit, then do the reverse, so that any improvement can be attributed to one side.

How does Parabolic SAR differ from other trailing stops such as Supertrend or an ATR stop?

The trail distance comes from a different place. ATR-based stops, including Supertrend, set their offset from a volatility estimate, so the band widens when ranges expand and narrows when they contract. Parabolic SAR ignores volatility: its distance is a function of how long the direction has persisted and how often new extremes have appeared, which means the stop can be tightening into an expanding market or sitting loose in a quiet one. The practical consequence is that SAR tends to give back less at the end of a sustained run but adapts poorly to a volatility regime change, while ATR-based trails do the opposite. Versions that combine them are usually exploiting that difference rather than seeking confirmation, since two stops measuring the same thing would fail together.

Why do two platforms draw different Parabolic SAR dots with identical settings?

Because the published rules leave several details to the implementer. How the first direction and extreme point are seeded at the start of the series is the most common cause, and its effect can persist for many bars. Implementations also differ on whether the new SAR is clamped so that it cannot penetrate the previous one or two bars' range, which Wilder specified but not every version applies, and on whether the initial acceleration equals the step. Running the calculation on Heikin Ashi or Renko series instead of standard candles is a third cause and a larger one. When comparing versions, reconcile these before concluding that a parameter difference explains the gap.

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