Trendlines have a specific problem no other technical tool shares: two competent traders drawing on the same chart will produce different lines. That subjectivity is worth confronting directly, because it determines how much weight a trendline deserves — which is less than most guides suggest.

What a trendline is

A diagonal line connecting a series of swing points, representing dynamic support or resistance.

In an uptrend, the line connects rising swing lows and sits beneath price. In a downtrend, it connects falling swing highs and sits above.

The underlying idea is the same as horizontal levels: participants act at the line, producing orders that halt or reverse price. The difference is that the level moves over time.

The subjectivity problem

Horizontal support at 1.0850 is 1.0850 for everyone. A trendline depends on which swing points you connect, whether you use wicks or bodies, and how far back you start.

Change any of those and the line sits somewhere else.

None is objectively correct. This means a trendline “holding” or “breaking” is partly a function of how you drew it, which is a genuine weakness.

Rules that reduce the problem

Trendlines remain useful if you constrain how you draw them.

Three touches minimum. Two points define a line mathematically — any two points do. The third touch is what suggests participants are actually reacting there. A two-touch trendline is a line you drew, not a level the market recognises.

Pick wicks or bodies and never switch. Wicks capture extremes; bodies capture where price settled. Both are defensible. Alternating between them means you can always find a line that fits.

Do not redraw after entering. If the line breaks, the setup is invalid. Write this down as a rule, because it will not feel obvious in the moment.

Prefer shallower lines. A very steep trendline reflects an unsustainable rate of advance and will break quickly regardless of whether the trend continues. Steep lines produce false break signals.

What a trendline break actually means

Less than most traders assume.

A broken trendline means the rate of advance has slowed. It does not mean the trend has ended.

Price can break a steep trendline and continue upward at a gentler angle, forming a new, shallower trendline. The first line broke; the uptrend did not.

This is why trendline breaks should be read alongside structure. A trendline break plus a break of structure is a meaningful signal. A trendline break alone is a change in pace.

Traders who exit trends on trendline breaks alone frequently exit healthy trends that simply decelerated.

Channels

A channel adds a parallel line on the opposite side of price, creating a corridor.

In an ascending channel, the lower line connects swing lows and the upper line runs parallel above, touching swing highs. Price oscillates between them while advancing.

Channels are useful for two things:

Context. Price near the lower line in an ascending channel is relatively low within the trend — a better location for a long entry than price near the upper line.

Targets. The opposite line provides a natural target for a position entered at one side.

The same subjectivity applies, compounded — you are now drawing two lines rather than one. Channels that require adjustment to keep price inside are not describing anything real.

Trading with trendlines

Used as one input among several rather than as a primary signal.

Note the stop placement. Structure provides a firmer invalidation point than a line whose position depends on drawing choices. The trendline identified the location; structure defines where the idea is wrong.

Where trendlines fail

In ranges. Diagonal lines drawn through sideways price connect points that have no relationship. The lines look valid and mean nothing.

On low timeframes. Swing points form constantly, so trendlines can be drawn almost anywhere. The subjectivity problem is at its worst here.

When too steep. Unsustainable angles break early and often, producing false signals about trend health.

After news. A repricing moves price through lines without regard to them.

An honest assessment

Trendlines are a secondary tool. They are useful for visualising the rate and shape of a trend, and for identifying areas where a pullback might find support.

They are weaker than horizontal levels, which are objective, and weaker than structure, which gives a definitive invalidation point. A trader who dropped trendlines entirely and relied on horizontal levels plus structure would lose very little.

That is not a reason to avoid them. It is a reason not to build a method around them, and to treat a trendline break as information rather than a signal.

What to do next

The next lesson covers chart patterns — the larger formations built from structure and levels, and an honest look at how reliable they actually are.

Frequently asked questions