Parabolic SAR: how stop-and-reverse works, step by step

The Parabolic SAR is a trailing stop that never stops trading. J. Welles Wilder Jr. introduced it in 1978, in the same book as the RSI and the Average True Range, as the "Parabolic Time/Price System." SAR stands for stop and reverse: the indicator places a stop below price in an uptrend and above price in a downtrend, and when price touches the stop, the position flips to the other side and a new stop appears on the opposite side.

On a chart it shows up as a series of dots that trail behind price and speed up as a trend extends, curving toward price like a parabola. It is excellent at staying with a strong trend and at protecting gains, and it is famously poor in sideways markets. This guide walks through the calculation bar by bar on Alphabet's 2026 chart and then shows the honest year-long record of trading every flip.

The idea: time as well as price

Most trailing stops move only when price moves. Wilder wanted a stop that also tightened with time: the longer a trend runs, the less room it gets. So the SAR moves toward price every bar, even on a quiet day, and moves faster each time the trend makes a new extreme. A trend that stalls is soon caught by its own stop.

Three quantities drive it:

• SAR: the stop level for the current bar.
• EP (extreme point): the highest high of the current uptrend, or the lowest low of the current downtrend.
• AF (acceleration factor): how far the SAR moves toward the EP each bar. It starts at 0.02, increases by 0.02 each time a new EP is set, and is capped at 0.20.

The formula

A worked example on Alphabet

Alphabet (GOOGL) slid through March 2026 to a low of $272.11 on March 30, the extreme point of that downtrend. On April 1 the stock traded up to $300.52, above the SAR that was falling toward it, and the system flipped to long. Here are the following bars, using Finabase's daily data.

Every SAR in bold matches Finabase's chart. On the flip day the SAR is placed at the old downtrend's extreme, $272.11. On April 2 there was no new high, so the AF stayed at 0.02 and the SAR crept up 57 cents. From April 6 each new high added 0.02 to the AF, and the SAR's daily step grew: $1.09, then $1.88, then $3.67. That acceleration is the parabola.

The SAR on a real chart

The April flip was the SAR at its best. From the April 1 close of $297.39 to the May 12 flip back to short at $387.35, the long leg gained 30.2%, and the rising SAR locked in more of the move each week.

The rest of the year shows the other side. Alphabet ended the period almost exactly where it began, up 0.8%, after rallying to $408.61 in May and giving most of it back. In that kind of market a stop-and-reverse system is whipsawed repeatedly.

Treating every flip as a trade at the closing price (a simplification; real fills happen at the SAR level, intraday) gives this record:

One great trend paid for most of the year's whipsaws, and not quite all of them. That is a typical profile for the SAR: a low win rate, a few large winners, and a strong dependence on whether the market trends.

How traders use the Parabolic SAR

As a trailing stop. The most durable use is not the reversal but the stop. Enter on some other evidence, then trail the stop at the SAR. The acceleration means a mature trend gets less and less slack, which protects open gains.

With a trend filter. Wilder himself recommended applying the SAR only when a market is trending, and he designed the Directional Movement System (ADX) partly for that purpose. Many traders take only the long flips when price is above a rising 200-day moving average and only the short flips below a falling one. On the Alphabet year, simply ignoring the short legs turned a small loss into a gain.

Adjusting the acceleration. A smaller step (0.01) gives trends more room and flips less often; a larger step (0.03) or maximum (0.3) hugs price tighter and flips more. Change it deliberately, and check the effect on more than one chart.

Pitfalls and limitations

Sideways markets. Because the SAR is always in the market, every range produces a string of small losses.

Gaps. The SAR is evaluated against the bar's range. A gap through it fills at the open, which can be far worse than the SAR level shown.

The starting point matters. The first trend direction and EP depend on where the calculation begins; different platforms can show different dots for the first few bars.

Comparison with other trailing methods

For the moving-average version see Simple moving average (SMA): formula, crossovers and limits; for a momentum view to pair with the SAR, see Relative Strength Index (RSI): how to read and use it.

How Finabase calculates and scores the Parabolic SAR

Finabase computes the SAR with TA-Lib's SAR function on each bar's high and low. The study, listed as "PSAR" or "Parabolic SAR," defaults to an acceleration of 0.02 and a maximum acceleration of 0.2, Wilder's values, and draws the SAR as dots on the price chart. The ready-made "Parabolic SAR" chart template pairs it with a 63-day SMA, MACD and RSI.

In the technical gauge, the SAR is an overlay row: a close at or above the SAR counts as Bullish (labelled a buy signal), a close below it as Bearish (a sell signal). The Scanner lists stocks whose close crossed the SAR at the default settings, with the date, which is a quick way to see the day's flips across a market. As the Alphabet record shows, a flip is a change of state, not a forecast.

Frequently asked questions

What does SAR stand for?

Stop and reverse. The indicator gives a stop level; when price reaches it, the original system closes the position and opens one in the opposite direction.

What are the best Parabolic SAR settings?

Wilder's 0.02 step and 0.2 maximum remain the standard and are Finabase's defaults. Smaller values suit slower, longer trends; larger values suit short-term trading but flip more.

Is the Parabolic SAR a good indicator?

It is a good trailing stop in trending markets and a poor stand-alone system in ranges. On Alphabet's 2026 chart, one 30% trend accounted for nearly all the gains of 25 flips.

Why do the dots jump to the other side of price?

Because price traded through the stop. The SAR then restarts on the other side at the previous trend's extreme point, with the acceleration factor reset to 0.02.

Summary

The Parabolic SAR is a stop that moves toward price every bar and faster with each new extreme, then flips when price reaches it. The Alphabet example shows the mechanics to the cent and the trade-off in full: a 30% trend captured cleanly, inside a year of 25 flips and only 7 winners. Use it to trail a trend you already believe in, and filter out the flips that go against the bigger picture.