Parabolic SAR: dots, acceleration factor and trailing logic

Parabolic SAR is the indicator that draws a row of dots below or above the candles. Dots below price mean the indicator considers the trend up; dots above mean down. When price touches the dots, they flip to the other side. It is simple to read, which is exactly why it is worth understanding what it actually does before trusting it.

What SAR stands for

SAR means "stop and reverse". J. Welles Wilder designed it in the 1970s as a trailing stop for a trader who is always in the market: long until the stop is hit, then immediately short, and so on. The dots are the stop level. The trailing stop glossary entry explains the underlying idea.

So Parabolic SAR does not try to predict anything. It answers one question: "If I were following this trend, where would my exit be now?"

How the dots are calculated

Three ingredients:

• SAR: the current dot.
• EP (extreme point): the highest high of the current uptrend, or the lowest low of the current downtrend.
• AF (acceleration factor): starts at 0.02, increases by 0.02 every time a new extreme point is made, and is capped at 0.2.

Each new dot is: next SAR = current SAR + AF × (EP − current SAR).

In plain words, the dot moves a fraction of the distance towards the extreme price. Early in a trend that fraction is small (2%), so the dots lag far behind. Each new high or low increases the fraction, so the dots accelerate towards price, which gives the curved, parabolic shape. When price crosses the dot, the trend flips, the new SAR is placed at the previous extreme point, and AF resets to 0.02.

A worked example

USD/JPY on M5 is in an uptrend. The current SAR is 151.000, the highest high (EP) is 151.500 and AF is 0.02.

• Next SAR = 151.000 + 0.02 × (151.500 − 151.000) = 151.010. The dot creeps up by one pip.
• The next candle makes a new high at 151.600, so AF becomes 0.04. Next SAR = 151.010 + 0.04 × (151.600 − 151.010) ≈ 151.034.
• After several more new highs, AF reaches the 0.2 cap and each dot closes a fifth of the remaining gap, hugging price tightly.

Then a pullback candle dips to 151.450 while the dot is at 151.480. The dot is touched, SAR flips above price at the last extreme point, and the indicator now says "downtrend". Whether that was the true end of the trend or just a pullback, the indicator cannot know.

What the settings change

The defaults 0.02 (step) and 0.2 (maximum) are Wilder's. Raising the step makes dots catch up faster: earlier exits, more flips. Lowering it keeps dots further away: fewer flips, but later reaction to genuine reversals. There is no setting that is both quick and free of false flips; you just choose which mistake you prefer.

Whipsaws in ranges

Parabolic SAR assumes the market is always trending. In a sideways range, price swings back and forth through the dots, and the indicator flips every few candles. Each flip looks like a fresh signal, and each is late, because it happens only after price has already moved against the previous side.

A typical pattern in a quiet session: dots flip to bullish near the top of the range, then to bearish near the bottom, then bullish again near the top. Following them would mean buying high and selling low repeatedly. That is why many traders filter SAR with a trend-strength measure such as ADX and ignore flips when ADX is low.

Short expiries

On S15 or M1 charts, tick noise alone can touch the dots, so flips become very frequent. Because a flip only occurs after price has crossed, the signal arrives after the move that caused it. For a short expiry, that lag matters more than on longer horizons: the move you are reacting to may already be the whole move.

If you use SAR, it is usually more readable on M5 or higher as a description of the current trend, combined with price structure and moving averages.

On Sky Trade's OTC instruments, prices are generated by Sky Trade's server and do not follow any real market. The model makes the next move unpredictable, so SAR flips there simply track random swings.

How to use it in the Sky Trade terminal

Parabolic SAR is in the trend group of the indicators list. Start with the default settings and watch how many flips occur on M1 versus M5 of the same market pair; the difference is instructive.