This calculator does not just tell you the date of the next clock change — it estimates how many days your own body is likely to need to catch up, and gives you a plan to start before the clock does.

Start by picking your region: the date and direction of the next transition differ by country, and Australia and New Zealand run on different rules from each other despite both being in the Southern Hemisphere. Add your usual bedtime and wake time on a normal weeknight — these personalize the night-by-night plan further down the page; they do not change the estimated adjustment window itself, which comes from the rhythm and light questions below.

The three quick questions build a light read on your rhythm and your daily light exposure. Chronotype (morning, midday, or evening-leaning) changes how fast your internal clock re-entrains: later chronotypes consistently need more time, especially after a forward shift. Daytime and evening light matter separately — more daytime light outdoors speeds up the adjustment, while brighter light during the evening slows it down. The three daytime and evening light options are simplified stand-ins for specific light levels used in the underlying research, not a measurement of your actual light exposure. Run it with a balanced rhythm, mixed daytime light, and normal evening lighting facing a forward shift, and the calculator itself outputs a 7–14 day window — that number comes from the model above, not from a separately published table, and your own answers will land somewhere else in the range.

Press “See my adjustment forecast” and your estimated adjustment window appears first — a range, not a single invented number, because individual variation here is genuinely large. Right below it, the Clock Gap shows your body clock and your social clock as two separate tracks, out of sync by about an hour right after the transition; the diagram is schematic, not drawn to a literal minute-by-minute scale.

Your biggest lever names whichever one factor — daytime light or evening light — is costing you the most days right now, with the estimated days you could shave off by changing it.

Your preparation plan divides the AASM’s general guidance to shift sleep gradually into specific bedtimes and wake times, listed in the order the nights actually happen — starting tonight and ending on the night right before the change — the per-night step size is our own division of the full hour across your available nights, not a specific interval published by AASM itself. The comparison line underneath spells out the difference: without a plan, the full hour lands all at once on transition day; with one, your schedule has already started moving.

If the next transition on your calendar is months away, the preview toggle lets you see an estimate for the other direction of the shift, without a specific date attached, so the calculator stays useful outside the two weeks a year the clocks actually change.