Parabolic SAR Explained: How to Trail Stops and Spot Trend Reversals

Most indicators tell you when to get in. The Parabolic SAR is built around the harder question: when do I get out? Its dots trail price and tighten as a trend ages, giving you an objective, rule-based trailing stop instead of a gut feeling.

This guide covers how the Parabolic SAR works, what the default settings mean, how to read the dots, where it breaks down, and how to turn it into a workflow with alerts.

What Is the Parabolic SAR?

The Parabolic SAR (Stop and Reverse) was created by J. Welles Wilder and published in his 1978 book New Concepts in Technical Trading Systems, the same book that introduced RSI, ATR and ADX. It plots a dot for every bar:

• Dots below price suggest an uptrend
• Dots above price suggest a downtrend

When price touches or crosses the dot, the trend is considered reversed. The dots flip to the other side of price and start trailing in the new direction. The name is literal: you stop the old position and reverse into the new one.

How the Calculation Works

You never need to compute it by hand, but the logic explains the indicator's behavior. For an uptrend, each new SAR value is:

Next SAR = Prior SAR + AF × (Extreme Point − Prior SAR)

• Extreme Point (EP) is the highest high of the current uptrend (the lowest low in a downtrend)
• Acceleration Factor (AF) starts small and increases each time price makes a new extreme point

Because AF rises as the trend makes new highs, the dots move faster and faster toward price. The path curves, which is where "parabolic" comes from. Early in a trend the stop sits far away and gives price room. Later it tightens, which locks in gains but also makes a reversal signal more likely on a routine pullback.

The Default Settings

Wilder's original parameters are still the standard on most platforms:

With these values, AF reaches its 0.20 cap after ten consecutive new extremes. Raising the step or maximum makes the indicator hug price tighter and flip more often. Lowering them gives price more room but exits later. There is no universally best setting; the right values depend on how volatile the stock is and how long you intend to hold.

Three Ways to Use It

1. As a trailing stop. Raise your stop to the latest SAR value each day. In an uptrend the stop only ever moves up.
2. As a trend-state filter. Only take long setups while dots are below price, and only short setups while they are above.
3. As an exit trigger. Close or reduce a position when the dots flip against you, then wait for your own entry rules before re-entering.

For a deeper look at stop methods generally, see our trailing stop loss guide and stop-loss orders explained.

Where Parabolic SAR Falls Short

• Whipsaws in sideways markets. When price chops in a range, it keeps crossing the dots and each flip is a false signal. This is the indicator's main weakness.
• It always has a position. SAR is always either long or short, so it gives no "stay out" signal.
• It exits on volatile pullbacks. In a strong trend, a normal pullback late in the move can tag the tightened dots and shake you out early.
• It lags. The dots follow price; they do not predict it.

The standard remedy is a trend filter. Check that the market is actually trending with the ADX indicator: when ADX is below roughly 20, ignore SAR flips. Sizing the initial risk with the average true range also helps you decide whether a SAR stop is too tight for that stock.

A Simple, Testable Setup

1. Trend: price above a rising 50-day moving average
2. Strength: ADX above 25
3. Entry: your own trigger, such as a pullback to the average or a breakout
4. Exit: SAR dots flip above price, or your fixed stop is hit, whichever comes first

Write the rules down, then test them on past data before risking money. Our guide on how to backtest a trading strategy covers sample size and overfitting, and a trading journal shows whether the rules work in practice.

Using Alerts With Parabolic SAR

SAR needs you to check the chart at the right moment, which is where alerts remove the screen time:

• Alert on the SAR level. At the end of each day, note where tomorrow's dot sits and set a price alert at that level. If price reaches it, you get notified and can review the exit.
• Alert on the setup. Set a price alert at your breakout or pullback level so you only open the chart when something happens.
• Update as the trend ages. Because the dots move every bar, refresh the alert level as the stop tightens.

New to alerts? Start with how to set stock price alerts. For shorter timeframes, see our day trading alerts setup guide.

Key Takeaways

• Parabolic SAR plots dots that trail price and flip when the trend reverses
• Dots below price suggest an uptrend; dots above suggest a downtrend
• Wilder's defaults are 0.02 start, 0.02 step and 0.20 maximum acceleration factor
• It works best as a trailing stop and exit tool in trending markets
• It whipsaws in sideways markets, so pair it with a trend filter like ADX
• Price alerts at the SAR level and at your setup level cut down on chart watching

This article is educational and not investment advice. Technical indicators do not predict future prices, and trading carries a risk of loss. Settings shown are Wilder's published defaults, not recommendations.