Definition
Harmonic patterns are chart formations defined not by their visual shape alone but by precise mathematical relationships between their parts. Patterns such as the Gartley, Bat, Butterfly, and Crab consist of a series of connected price swings whose lengths must satisfy particular Fibonacci ratios for the pattern to qualify.
Where a classic pattern like a triangle is identified loosely by eye, a harmonic pattern is identified by measurement. Each leg of the formation is checked against required retracement and extension ratios. Only when those ratios fall within tolerance is the pattern considered valid and a potential reversal zone defined.
Why it matters
How it works
A harmonic pattern is typically traced through five turning points connected by four legs. The analyst measures each leg and verifies that the retracement and extension ratios match the template for the specific pattern — a Gartley and a Bat, for example, differ mainly in their required ratios. Charting tools or pattern-recognition software handle much of this measurement.
When the ratios align, the pattern points to a potential reversal zone — a price region where the formation predicts a turn. Traders watch that zone for confirming behavior before acting. Because harmonic patterns rely so heavily on Fibonacci numbers, they are closely related to the broader use of Fibonacci retracements in technical analysis.