Concept

Crab

Crab, also known as Deep Crab, is a Elliott & Harmonics concept.

What is a Crab?

The Crab is the most extended of the standard XABCD harmonic patterns, introduced by Scott Carney in 2000. B retraces 0.382 to 0.618 of the XA leg, C retraces 0.382 to 0.886 of AB, and D completes well beyond the X extreme at a 1.618 extension of XA, typically confluent with a 2.618 to 3.618 projection of BC (see the harmonic ratio set). The Deep Crab variant permits a deeper B at 0.886 of XA while keeping the same 1.618 completion.

The Crab belongs to the second generation of harmonic patterns. H.M. Gartley drew the original retracement structure in Profits in the Stock Market (1935), and later authors attached Fibonacci ratios to its legs; Scott Carney's contribution, in The Harmonic Trader (1999) and the subsequent Harmonic Trading volumes, was to define distinct patterns by exact ratio combinations. Carney has described the Crab as among the most precise structures in the harmonic toolkit, because its 1.618 completion leaves comparatively little ambiguity about where the pattern is right or wrong.

In Carney's treatment the terminal CD leg tends to arrive fast and stretched, so the 1.618 zone is watched for sharp snap-back reactions rather than gradual turns; the completion functions as a potential reversal zone with invalidation beyond it. As with every harmonic completion, the level is a place to evaluate a reversal with defined risk, not a ceiling or a floor.

Like all XABCD structures the Crab prints in two orientations. A bullish Crab starts from a low at X, rallies to A, and completes when the CD leg drives below X to the 1.618 extension of XA; the bearish version is the mirror image, completing above X. The A-to-D portion also contains an ABCD structure, typically an extended variant given the Crab's long terminal leg, and harmonic practice treats the overlap of these independent measurements at D, rather than any single number, as the completion argument.

How to identify a Crab pattern on a chart

The Crab is measured, not eyeballed. Work leg by leg with a Fibonacci retracement and extension tool.

  1. 1Mark the XA leg: a strong initial move, often impulsive in character, that sets the pattern's origin and measurement base.
  2. 2Check B: it must retrace a shallow-to-moderate 0.382 to 0.618 of XA. A B near 0.886 shifts the candidate to a Deep Crab, and a B beyond X voids the structure entirely.
  3. 3Check C: a 0.382 to 0.886 retracement of AB that holds inside A's extreme, keeping the internal ABCD intact.
  4. 4Project D: extend XA by 1.618 and BC by 2.618 to 3.618. A tight overlap of the two projections beyond X defines the reversal zone; wide disagreement is a reason to pass.
  5. 5Demand a reaction before entry: the terminal leg often arrives near-vertical, so wait for rejection behavior at the zone, such as a reversal candle, momentum divergence, or a failed push, rather than fading the move blind.

How it's calculated

A five-point harmonic reversal pattern whose completion point D forms at the 1.618 extension of the initial XA leg.

1. Mark five alternating swing points X, A, B, C, D (bullish Crab: X low, A high, B low, C high, D low beyond X; bearish is the mirror image).
2. Validate B: abs(A - B) / abs(A - X) between 0.382 and 0.618, so AB retraces 38.2% to 61.8% of XA.
3. Validate C: abs(B - C) / abs(A - B) between 0.382 and 0.886.
4. Validate the BC projection: abs(C - D) / abs(B - C) between 2.618 and 3.618.
5. Validate the XA extension: abs(A - D) / abs(A - X) = 1.618, placing D beyond X (the defining Crab ratio).
6. The zone where the 1.618 XA extension and the BC projection overlap is the PRZ; the pattern completes when price trades into it, and a reversal away from D is the anticipated outcome.
X: pattern origin (swing low in a bullish Crab, swing high in a bearish one)
A: end of the initial impulse leg from X
B: first corrective swing, a partial retracement of XA
C: corrective swing retracing part of AB
D: completion point, beyond X
XA, AB, BC, CD: legs named by their start and end swing points
abs(): absolute value, so each ratio applies to bullish and bearish cases alike
PRZ: Potential Reversal Zone, the price area around D where the ratio targets converge

Ratios follow Scott Carney's definition (introduced in 2000); platforms typically allow small tolerances around each value.

Deep Crab variant: B sits at 0.886 of XA and the BC projection widens to 2.24 to 3.618, while D stays at the 1.618 XA extension.

The 1.618 XA completion distinguishes the Crab from the Butterfly, which completes at 1.272.

How traders use it

  • To fade climactic extensions: traders wait for price to reach the 1.618 XA projection, often after a near-vertical CD leg, and demand rejection behavior there before positioning against the move.
  • To ladder targets: entries at D sit far from the pattern's origin, so profit-taking is commonly staged at successive retracements of the AD swing instead of a single objective.
  • To separate candidates: scanners distinguish Crab from Butterfly setups by the B retracement (0.618 or less versus 0.786) together with the D projection (1.618 versus 1.27 of XA), and flag the Deep Crab when B sits near 0.886.
  • As a wave-count cross-check: a terminal CD leg into a 1.618 extension can coincide with the end of a five-wave impulse or the C wave of a corrective structure, and Elliott-inclined traders use agreement between the two frameworks to upgrade the setup.

Crab vs neighboring harmonic patterns

Butterfly: Both complete beyond X, but the Butterfly finishes at 1.27 of XA with a 0.786 B, while the Crab runs to 1.618 with a shallower B; misjudging B invites treating a 1.27 touch as complete while a Crab is still extending.

Bat: Both use the 0.886 ratio, in different roles: it is the Bat's D completion inside XA, but the Deep Crab's B retracement before a 1.618 extension beyond X.

Gartley: The Gartley completes inside the XA leg at a 0.786 retracement with B at 0.618, a shallower and more trend-friendly structure. The Crab completes far beyond X, so the two sit at opposite ends of the harmonic spectrum: retracement entry versus extension fade.

Three Drives: Three Drives shares the Crab's taste for terminal extensions but is built from three roughly symmetrical pushes, each completing at 1.27 or 1.618 of the prior correction, rather than a single XABCD skeleton. Both express exhaustion; they simply count it differently.

Concept family

Elliott & Harmonics

33 concepts mapped · 33 in the Library

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