Session Highs & Lows

Reference levels that track the running high and low of a defined trading session such as Asia, London, or New York.

What it is

Session highs and lows are reference levels that track the highest high and lowest low printed during a defined slice of the trading day — most commonly the Asian, London, and New York sessions in forex, which trades continuously across time zones. Because forex has no single exchange open or close, traders partition the day themselves, and the extremes of each partition become levels that many participants watch: the Asian range before London opens, the London high and low before New York, and so on. To plot them in Pine Script you define a session window (for example 00:00–09:00 in a chosen time zone), detect which bars fall inside it using the time() function with a session string and time-zone argument, and update a running high and low while the session is active. The subtle part is not the max/min logic — it is time handling. Session strings, time-zone names, and daylight-saving transitions are the leading source of silent bugs in session scripts: a hardcoded UTC offset that ignores DST will draw the 'London session' an hour off for half the year. These levels describe where price has traded; they do not predict where it will go. This material is educational only, not financial advice, and trading carries risk of loss.

How it works

The implementation has three parts. First, session membership: Pine's time(timeframe.period, session, timezone) returns na for bars outside the session window, so 'not na(...)' is a clean boolean for whether the current bar belongs to the session. Using an IANA time-zone name such as "Europe/London" or "America/New_York" — rather than a fixed offset like "UTC+1" — is what makes the script survive daylight-saving transitions, because IANA zones encode the DST rules. Second, session-start detection: the first bar where the membership flag turns true after being false marks a new session, and that is where the running high and low reset to the current bar's high and low. Third, accumulation: on every subsequent in-session bar, the stored high is the maximum of itself and the bar's high, and likewise for the low. The stored values persist across bars using var declarations, which is legitimate state-keeping rather than signal manipulation. Plotting with a line-break style keeps the levels from connecting across the gap between sessions. Everything here is deterministic and computable live on bar close — nothing about the construction needs future data, which makes correctly written session levels naturally non-repainting for completed bars (the current session's extremes update while the session is open, by definition).

How traders read it

• The Asian range (its high and low) is often watched as a pre-London reference: a narrow overnight range describes low overnight activity, nothing more.
• A push through a prior session's high or low tells you price has exceeded that session's extremes — it is a factual statement about traded range, not a confirmed 'breakout signal'.
• Price trading back inside a prior session range after poking beyond it is often labeled a 'sweep' or 'fakeout'; treat these labels as descriptions applied after the fact, not predictions.
• Compare session ranges over several days: whether volatility concentrated in London or New York recently is context, not a schedule the market must follow.
• The current session's high and low are provisional until the session closes — they can only expand while the session is live.
• If levels look shifted by exactly one hour, suspect a DST bug in the script's time-zone handling before suspecting the market.

Common settings

Typical windows (stated in local market time, using IANA zones): Asia roughly 00:00–09:00 Tokyo time, London roughly 08:00–17:00 "Europe/London", New York roughly 08:00–17:00 "America/New_York". Definitions vary by trader and by source, so any script should expose the session string and time zone as inputs rather than hardcoding them. Session levels are intraday tools — they are typically drawn on charts of 1 hour and below, since the session structure is invisible on daily bars.

Strengths

• Fully deterministic: given the same session definition and data, everyone computes identical levels — nothing subjective to interpret.
• Naturally non-repainting when written correctly, because the levels are built only from bars already closed within the session.
• Reflects a real structural feature of forex: liquidity and participation genuinely rotate across Asia, London, and New York.
• Useful shared reference points, since large numbers of participants watch the same session extremes.
• A good teaching case for correct time handling in Pine — session strings, IANA zones, and DST all show up in one small script.

Pitfalls to watch

• Time-zone and DST bugs are endemic: scripts using fixed UTC offsets draw sessions an hour wrong for part of the year, and the error is silent — the chart still looks plausible.
• Session definitions are conventions, not facts: 'London open' means different things in different scripts, so two traders can watch different levels while using the same words.
• The live session's high/low are provisional and expand until the session ends; treating the current extreme as fixed is a subtle form of hindsight.
• Broker server time versus chart time zone mismatches shift everything; always verify which clock the data feed uses.
• Levels are descriptive: a session high is where price stopped trading, not a wall — price moves through session extremes constantly.
• On low-liquidity instruments or holidays, session ranges can be dominated by a handful of ticks and carry little information.

Pine v6 example

//@version=6
indicator("Session High/Low", overlay = true)

sess = input.session("0800-1700", "Session Window")
tz   = input.string("Europe/London", "IANA Timezone", options = ["Europe/London", "America/New_York", "Asia/Tokyo", "UTC"])

// IANA zone names handle DST correctly; fixed UTC offsets do not
inSess  = not na(time(timeframe.period, sess, tz))
newSess = inSess and not inSess[1]

var float sHi = na
var float sLo = na
if newSess
    sHi := high
    sLo := low
else if inSess
    sHi := math.max(sHi, high)
    sLo := math.min(sLo, low)

plot(inSess ? sHi : na, "Session High", color = color.teal,   style = plot.style_linebr)
plot(inSess ? sLo : na, "Session Low",  color = color.maroon, style = plot.style_linebr)

Pro tip: Validate the time handling before trusting any session level: pick a date just after a daylight-saving change and check on the chart that the session shading still starts at the intended local hour. A script that uses "UTC+1" instead of "Europe/London" will pass this test in winter and fail it in summer. Session extremes are context about where trading happened, not predictions about where it will happen next — this is educational content only, not financial advice, and all trading involves risk of loss.

Educational only — not financial advice, not a recommendation to trade. No indicator is predictive; trading involves substantial risk of loss.