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Key Takeaways
- An uptrend line connects rising swing lows, while a downtrend line connects falling swing highs.
- Two pivots draw the line; each later reaction at it, a bounce or a break, tells you whether the market still trades it.
- Fix the price input, pivot rule and chart scale before you draw, because each one moves the line.
- A break is price crossing the line under the rule you trade: a touch intrabar or a completed close.
- Trade only confirmed pivots: the session 7 low becomes usable at session 9, two closes later.
What is a trendline?
A trendline is a straight line drawn through selected price pivots and extended through time to show a trend’s direction and pace. An uptrend line connects rising swing lows and a downtrend line connects falling swing highs, so the line becomes a changing support or resistance reference that a later close can break.
Choose the price series, timeframe, pivot rule and scale. An arithmetic line measures dollar change per time unit. A straight line on a log-price chart measures constant proportional change.
How to draw a trendline: pivots and confirmation
A two-bar swing-low rule requires the selected close to be below the two closes on each side. The pivot is located at that close, but becomes known only when the second following bar completes.
The $40 pivot at session 1 has two higher closes before it, $42 and $41, just off the left edge of the chart; the next two closes, $41.40 and $42.60, confirm it at session 3.
The $43 low at session 7 is below the two closes on each side and is confirmed at session 9, the first bar where a trader can draw the line from confirmed pivots.
Formula
Arithmetic slope m = (p₂ − p₁) / (t₂ − t₁); line price at t = p₁ + m(t − t₁), with t₂ ≠ t₁.- Positive slope represents an upward line and negative slope represents a downward line.
- Use the same price units and time coordinate. A straight line on a logarithmic price chart interpolates log prices instead.
Trendline example: slope, projection and break
Closing-price lows are $40 on session 1 and $43 on session 7. A low requires two higher closes on each side, so the second pivot is confirmed at session 9. The arithmetic line then projects to session 13.
- ($43 − $40) / (7 − 1) = $0.50 per session slope
- $43 + (6 × $0.50) = $46 projected line value on session 13
- $45.70 close = $0.30 below the projected line
The line rises $0.50 per session and reaches $46 on session 13. The $45.70 close is $0.30 below it. On a closing-cross rule, that session is the trendline break.
On a completed-close rule, session 13 is the break, and a long position that used the line as its stop exits there.
Arithmetic vs logarithmic trendlines
On a log-price chart, the same anchors give a per-session log slope of [ln(43) − ln(40)] / 6. At session 13, the projected price is $43 × ($43 / $40) = $46.23.
Count time the same way on both anchors and the projection: session numbers and calendar days give different lines.
How traders use trendline breaks
Choose the event that activates the setup: a reaction at the line, a close through it or a later retest. Record the entry, invalidation, size and target. A sloped line sits at a new price every bar, so date the scenario: the Options Profit Calculator shows each structure’s payoff at the target and its value where the line will sit on your exit date.
Compare subsequent swings with Support and Resistance. A setup can require both events in sequence: the close through the trendline first, then a break of the prior horizontal swing low.
Limitations of trendlines
- Fix the series, pivot rule, timeframe and scale before you trade the line: the same anchors project $46 on an arithmetic chart and $46.23 on a log chart.
- Draw the line only from confirmed pivots. The session 7 low becomes usable at session 9, so a line drawn with hindsight can look cleaner than the one available in real time.
- Let the market vote on the line. Two pivots draw it, and each later bounce or break shows whether price still trades it.
- Plan for a false break and a retest. A close through the line can be followed by a return to the other side, and the prior horizontal swing low stays intact until price breaks it too.
Bottom line
A trendline turns two pivots into a sloping reference level that shows a trend’s direction and pace. Fix the price series, pivot rule and scale before drawing, anchor the line only on confirmed pivots, and define the reaction, close or retest that turns the line into a trade.
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Sources and Further Reading
How entries are sourced, calculated and updated: editorial methodology.