A trendline is the most subjective tool in technical analysis. Two traders given the same chart will produce different lines, and both will be able to justify theirs. That is not a reason to avoid the tool — it is a reason to be strict about how you use it.
What a trendline is actually claiming
An upward trendline connects successive swing lows. It claims that buyers have been stepping in at a consistent rate — not a fixed price, but a rising one. A downward trendline connects swing highs and claims the same about sellers.
That is a stronger claim than a horizontal level makes. A horizontal level says "buyers appear at 1.0850." A trendline says "buyers appeared at 1.0850, then 1.0890, then 1.0930 — and they will appear at 1.0970 next week." Slope is an extrapolation, and extrapolations decay.
Two points draw a line; three make it a trendline
Any two points on a chart can be connected. That is geometry, not analysis. A line only becomes evidence when price has come back to it a third time and respected it — at that point the market has demonstrated something, rather than you having noticed a coincidence.
So the working rule: draw with two, trade with three. The third touch is the one that turns a hypothesis into a level other participants are also watching.
A related discipline: draw the line and then leave it alone. If you find yourself adjusting the anchor points because price closed slightly the wrong side, you are no longer analysing the chart. You are fitting a curve to it, and a line that has been refitted three times predicts nothing.
Wicks or bodies?
This argument never ends, and the answer is that it depends on what you are measuring.
Connecting wicks captures the extremes — every price at which the market turned. Connecting bodies (closes) captures where the market settled, ignoring intraday spikes that were immediately rejected.
Body lines tend to be cleaner and produce fewer false breaks, because a spike through a wick line is common and a close through a body line is meaningful. Wick lines mark the true boundary of where price has traded. Pick one convention, state it to yourself, and apply it consistently — the inconsistency is what causes damage, not the choice.
Channels
A channel is a trendline with a parallel copy on the opposite side of price. Draw the upward trendline across the swing lows, then clone it and place it across the swing highs, and you have a corridor.
Channels do two things. They give a rough target — at the lower rail in an uptrend, the upper rail is a plausible destination. And they flag a change of character: price that stops reaching the upper rail is losing momentum long before the lower rail breaks.
They are not boundaries. Price leaves them regularly, and a break of the upper rail in an uptrend is acceleration, not a sell signal — a common and expensive misreading.
Breaks, and what they are worth
A trendline break is the most-traded and least-reliable signal in this toolkit. Lines get broken constantly, and a break is only informative alongside the structural evidence from the previous lesson.
The filters worth applying:
- Require a close beyond the line, not a touch. Wicks through trendlines are routine.
- Check the structure. A broken trendline that has not also broken the last swing low is a change in pace, not in direction. The trend can simply continue at a shallower slope — and often does, on a new, flatter line.
- Distrust steep lines. A near-vertical trendline describes a move that cannot continue and will break almost immediately. It carries no information beyond "this went up fast."
- Watch the retest. A broken trendline that price returns to and fails at is far better evidence than the break itself.
The honest limitation
Trendlines are a way of seeing structure, not of proving it. They are best treated as a visual aid on top of the swing-high/swing-low reading, not as a signal generator in their own right. If a trendline and the structure disagree, the structure is the one with the objective definition.
What to take from this
- Up trendlines connect lows; down trendlines connect highs. The slope is an extrapolation.
- Draw with two touches, act on three.
- Pick wicks or bodies and stay consistent; never refit a line to save a view.
- A channel gives targets and early warning, not boundaries.
- Require a close through the line, and confirm against swing structure before calling a break.
Sloped lines describe the pace of a move. Horizontal ones describe the prices the market keeps returning to — which is the subject of the next lesson, and the more durable of the two ideas.