If support and resistance are the horizontal scaffolding of a chart, trendlines and chart patterns are the diagonal and geometric structures built on top of them. Trendlines turn a trend from a vague impression into a drawable, testable line. Chart patterns package recurring sequences of support, resistance, and trendline behaviour into recognisable shapes that hint at what is likely to come next.

What it is

A trendline is a straight line drawn along a series of swing points to capture the direction and slope of a trend. In an uptrend you connect the rising swing lows; the line acts as diagonal support beneath price. In a downtrend you connect the falling swing highs; the line acts as diagonal resistance above price. The trendline visualises the rhythm of the trend - how steeply it is advancing and where pullbacks have historically found buyers or sellers.

A chart pattern is a recognisable formation made of multiple swings, often bounded by trendlines or horizontal levels, that has historically resolved in a characteristic direction. Patterns fall into two broad families: continuation patterns, which represent a pause within an existing trend before it resumes (flags, pennants, ascending/descending triangles, rectangles), and reversal patterns, which mark the end of one trend and the start of another (head and shoulders, double tops and bottoms, rounding tops and bottoms).

How it works

Trendlines work for the same reason support and resistance work: participants watch them and act around them. When a stock has bounced off a rising trendline three times, traders anticipate the fourth bounce and place orders accordingly, which helps produce it. The slope encodes information too - a shallow trendline describes a sustainable, durable advance, while a near-vertical line describes an unsustainable blow-off that usually ends badly.

Patterns work because they are visual summaries of the supply-and-demand story. A symmetrical triangle, for instance, is simply buyers and sellers converging: each rally peaks a little lower and each dip bottoms a little higher, a coiling of energy that eventually releases in a sharp move. A head-and-shoulders top tells the story of a trend making one final exhausted push (the head) that fails to be matched (the right shoulder), signalling that buyers have run out of conviction. The shape is just a convenient label for a recurring behaviour.

How to use it

Drawing trendlines well

Good trendlines obey a few disciplines:

• Require at least two points to draw and a third to confirm. Any two points define a line; it only becomes meaningful once price respects it a third time.
• Connect the extremes that matter. In an uptrend connect the swing lows (the wicks or closes, but be consistent); in a downtrend connect the swing highs.
• Prefer the line that touches the most points cleanly over one that you have to force through the body of several candles.
• Use higher timeframes for the structural trend and lower ones only for fine-tuning. A weekly trendline outranks an hourly one.
• Accept that trendlines are approximate. Like support and resistance, they are zones drawn as lines; a small overshoot is not automatically a break.

Continuation versus reversal

The single most useful question with any pattern is: is this a pause or a turn? Continuation patterns form in the direction of the prevailing trend and resolve by continuing it - a bull flag after a strong rally usually breaks upward. Reversal patterns form at the end of an extended trend and resolve by reversing it - a double top after a long advance usually breaks downward. Misreading a continuation as a reversal (or vice versa) is one of the most common and costly pattern-trading errors.

Confirmation

No pattern is tradable until it is confirmed. A pattern is only a potential until price breaks the line that defines it - the neckline of a head and shoulders, the trendline of a flag, the support of a double bottom. The confirmation checklist:

1. A decisive close beyond the pattern boundary, not just an intrabar poke.
2. Supporting volume - genuine breakouts from patterns tend to expand volume; quiet breakouts are suspect.
3. A measured-move target and a defined invalidation. Most patterns suggest a rough target (e.g. the height of a head and shoulders projected down from the neckline) and a logical stop (back inside the pattern). If the trade no longer makes sense once you mark both, skip it.

Worked example

A stock trends up for two months, then carves out a sideways rectangle between $40 support and $44 resistance for three weeks while pulling back gently - a textbook continuation setup, since the prior trend was up. You mark both boundaries. The pattern is not yet tradable. Then price closes at $44.80 on volume well above its recent average, and the next session holds above $44. That is confirmation: prior resistance at $44 should now behave as support, the measured-move target is roughly the $4 box height projected upward to about $48, and your invalidation is a close back inside the box below $44. Had price instead spiked to $44.20 intraday and closed at $42 on light volume, you would have a failed breakout and no trade.

Strengths & limits

The strength of trendlines and patterns is that they impose structure on a noisy chart and give you a framework for both entry and risk. A confirmed pattern provides an objective trigger (the breakout), a target (the measured move), and an invalidation (back inside the pattern) - the three things every plan needs.

The limitations are real and worth respecting. Trendlines are subjective: give the same chart to ten traders and you will get ten slightly different lines, and it is easy to draw the line that flatters the trade you already want. Patterns are pattern-recognition, which the human brain does compulsively, so the temptation to see a head and shoulders in random noise is strong. And patterns fail - even textbook formations resolve against expectations a meaningful fraction of the time, which is exactly why confirmation and a predefined invalidation are non-negotiable. Treat patterns as probabilities with built-in exits, never as predictions.

Key takeaway: Draw trendlines from at least two points and confirm with a third; classify every pattern as continuation or reversal based on the prevailing trend; and never act until a decisive close - ideally on supporting volume - confirms the break, with a target and invalidation defined in advance.