Parabolic SAR

The Parabolic SAR ("Stop and Reverse") is Wilder's mechanical trailing-stop system in indicator form. It plots a single dot per bar - either above or below price - that follows price as the trend extends and "catches" it when the trend reverses. The acronym SAR is literal: when the dot touches price, you stop your current position and reverse direction.

Used inside a strongly trending market, PSAR is one of the most rule-based trailing-stop tools in technical analysis. Used in a chopping market, it generates a string of "flip" signals that produce losses on nearly every trade. The indicator works exactly as designed. The trader applying it without a regime filter is the one who loses money.

What PSAR actually measures

PSAR plots an accelerating curve that trails price. Each new extreme price (a higher high in an uptrend, a lower low in a downtrend) causes the curve to accelerate slightly closer to price. The curve never moves backward - it only follows the trend tighter as new extremes print.

When price finally retraces enough to cross the curve, the trend is considered ended. The SAR "flips" to the opposite side of price and starts trailing in the new direction. The flip is the signal: exit the current trade, optionally enter the opposite trade.

The curve's acceleration is what gives the indicator its name. As the trend extends, the dots get progressively closer to price - the trailing stop tightens. In a strong trend that runs for many bars, the dots can be quite distant from price in the early stages and very tight by the time the trend matures. This is by design: give a new trend room to breathe, then tighten as it proves itself.

The formula

SAR(today) = SAR(yesterday) + AF × (EP - SAR(yesterday))

where AF = Acceleration Factor (starts at 0.02, increases by 0.02 each time a new EP is set,
            capped at 0.20)
      EP = Extreme Point (highest high in current uptrend, or lowest low in current downtrend)

In an uptrend, SAR is below price and rises each bar. The AF starts at 0.02. Each time price prints a new high, the EP updates to that new high and the AF increases by 0.02 (up to a maximum of 0.20). The SAR moves toward the EP at a rate determined by AF.

When the SAR is breached (price closes below the SAR in an uptrend, or above in a downtrend), the trend reverses. SAR flips to the opposite side, AF resets to 0.02, and EP becomes the most recent extreme on the opposite side.

The formula is closed-form and deterministic. Every platform should produce identical PSAR values from identical OHLC data.

A worked example

Suppose we are in an uptrend. The current SAR is at 100.00. The extreme point (EP) is 105.00 (the highest high of this uptrend so far). The acceleration factor (AF) is 0.04 (it has been bumped twice from the starting 0.02 since two new highs have printed during this uptrend).

Today's bar prints a new high of 106.50. The new EP is 106.50. The new AF is 0.06.

Compute the next SAR:

SAR(next bar) = 100.00 + 0.06 × (106.50 - 100.00)
              = 100.00 + 0.06 × 6.50
              = 100.00 + 0.39
              = 100.39

The SAR steps up from 100.00 to 100.39. If price prints another new high tomorrow, the EP updates again, the AF bumps to 0.08, and SAR steps even closer to price.

If price drops sharply and closes below the SAR (currently around 100.39), the trend ends. SAR flips above price, AF resets to 0.02, and the EP becomes today's low. The indicator is now trailing a downtrend.

How traders actually use Parabolic SAR

Two uses generate edge. The third (treating every PSAR flip as a trade trigger) does not.

1. Trailing stop in a confirmed trend

PSAR's intended use. You enter a trend trade via your own signal stack (a breakout, a moving-average pullback, whatever). Once in the trade, use PSAR as your trailing stop:

• Long: stop at the PSAR dot below price. As the trend extends, the dot rises and the stop tightens.
• Short: stop at the PSAR dot above price.

When the SAR flips, you are stopped out. This produces a mechanical, rule-based trailing-stop discipline that prevents you from holding winners into giveback or holding losers past your invalidation level.

The acceleration is what makes this work in extended trends: a parabolic move that runs for 30 bars will see the SAR tighten significantly over time, locking in profit as the trend matures.

2. Filter for trend continuation entries

When SAR has been on one side of price for many bars without flipping, the trend is established. Pullback entries (to a moving average, to a key level) become higher-probability in that confirmed-trend regime.

Use PSAR not as the entry signal but as a "is this trend real?" filter. Combine with ADX > 25 for stronger confirmation.

The trap most retail traders fall into

The PSAR-flip-trading mistake. Most courses teach: "Buy on PSAR flip up, sell on PSAR flip down." In a ranging market, this produces a stream of losing trades back-to-back.

The reason is mechanical. PSAR is built to flip exactly when price retraces enough to cross the trailing dots. In a trending market, that requires a meaningful retrace. In a ranging market, every minor swing produces a flip. The indicator does what it does; the trader treating chop as trend is the problem.

Backtests of "PSAR flip strategies" on any reasonably noisy market produce devastating results. Win rates of 30 percent with average losses larger than average wins. The mechanics guarantee that in chop, PSAR flips occur right before price reverses again. Each flip is a near-perfect contrarian indicator at the local turn.

The fix is the standard one for all trend-following indicators: regime filter first. Only act on PSAR signals when ADX confirms trend (ADX > 25), when price is clearly above or below a long-term moving average, or when structure shows an actual trending market on the higher timeframe.

The second trap: changing the default settings. Wilder's 0.02 acceleration / 0.20 maximum is the universal convention. Lowering the acceleration makes PSAR slower and less protective; raising it makes PSAR jumpy and flip more often. The defaults are the equilibrium. Almost no one productively changes them.

PSAR vs other trailing stops

vs Chandelier Exit. Chandelier Exit = highest high since entry - (3 × ATR). It is ATR-based rather than acceleration-based. Chandelier gives a smoother, less aggressive trail than PSAR; PSAR tightens faster as trends mature. Chandelier is preferred when you want to give the trend more room; PSAR is preferred when you want to lock in gains aggressively.

vs Moving Average Trail. A 9-EMA or 20-SMA can serve as a trailing stop ("exit when price closes below the 20-SMA"). Smoother than PSAR but slower to react. MA trails miss the late-trend tightening that PSAR provides.

vs Fixed Percentage Trail. A 5% trailing stop is the simplest possible trail. Lacks PSAR's acceleration - never tightens. Easier to understand, worse at locking in profits.

vs Manual Structure-Based Stops. Trailing to the most recent swing low (in an uptrend) is the discretionary equivalent. More flexible than PSAR but requires real-time judgment. PSAR is the mechanical version.

Common questions

Should I change the acceleration factor? Almost never. Wilder's 0.02 / 0.20 is the universal default. If you change it, you are reading a different indicator than every other trader and most published research.

Why does PSAR flip so often on my chart? Because the market you are looking at is range-bound or low-volatility. PSAR is built for trending markets. In chop, frequent flips are baked into the math.

Does PSAR work on intraday charts? It can, in clearly trending intraday markets (the open of a strongly directional day, for example). On 1- and 5-minute charts during normal range-bound periods, PSAR flips too frequently to trade.

What does the "SAR" in Parabolic SAR mean? Stop and Reverse. Wilder designed it as a complete trade system: when the SAR flips, you stop your current position and reverse direction. This double-action ("stop AND reverse") is what made it a complete trading system in 1978 - rare for indicators of that era.

Can PSAR predict reversals? Not really. It catches reversals after price has crossed the dots. That is by design - PSAR is a trailing stop, not a forward-looking indicator. The "flip" is a confirmation that the trend has ended, not a prediction.

Why is PSAR shown as dots and not a line? By convention, to emphasize that each dot is a discrete data point - the stop level for that specific bar. A line would imply continuous interpolation, which is incorrect (the SAR steps in discrete jumps each bar).

When to use Parabolic SAR and when not to

Use PSAR when:

• You are in a confirmed trend and need a mechanical trailing stop
• ADX is above 25 and the market is clearly directional
• You want acceleration in your trail (tighter stops as the trend matures)

Skip PSAR when:

• The market is range-bound or chopping (PSAR flips become unprofitable)
• You are trading on a 1- or 5-minute chart in a non-trending intraday period
• You are using PSAR flips as entry signals without a separate regime filter - that combination loses money