Short answer
Your chronotype is your body clock’s natural timing – whether you are an early “lark”, a late “owl”, or somewhere in between. It is largely set by genetics and shifts with age. Chronotype influences how easily you handle travelling east versus west, because it partly determines when your internal night falls.
Simple explanation
Some people wake early, bright and ready, then fade in the evening; others struggle in the morning but come alive at night. These are the extremes of chronotype – “larks” and “owls” – with most people spread somewhere in between. It is not simply a habit or a choice: your chronotype reflects where your internal clock naturally sits, and pushing hard against it feels like a constant, mild version of jet lag even at home.
Chronotype also changes over a lifetime. Children tend to be early; teenagers shift dramatically later (which is why early school starts are so hard for them); and from adulthood onward people tend to drift gradually earlier again with age.
Deep dive
Chronotype is a property of your circadian rhythm – essentially, the phase your clock settles at relative to the day. Two established tools measure it. The Morningness-Eveningness Questionnaire (MEQ), developed by Horne and Östberg in 1976, scores preference through a set of questions. The Munich ChronoType Questionnaire (MCTQ), developed by Roenneberg and colleagues from 2003, instead uses your actual sleep behaviour, focusing on the mid-point of sleep on free days (when no alarm forces you up) as an objective anchor of timing.
Large datasets from the MCTQ (Roenneberg and colleagues, 2007) show chronotype is distributed roughly like a bell curve across the population, with substantial spread – the gap between strong larks and strong owls can be several hours of internal time. Genetics accounts for a large part of it, with age and light exposure as major modifiers. Because a late chronotype in a society built around early schedules produces a chronic mismatch between biological and social time, this everyday misalignment has its own name – social jet lag.
Chronotype interacts with the phase response curve through where your CBTmin sits. An owl’s temperature minimum falls later in the morning; a lark’s falls earlier. Since the light rules are all defined relative to CBTmin, two travellers on the same flight can need slightly different light timing. This is why jetlag.info asks for a simple chronotype input rather than assuming everyone is average – though it deliberately uses a short question rather than forcing a full MEQ.
Illustration (planned graphic)
A horizontal distribution (inline SVG) running from “early / lark” on the left to “late / owl” on the right, drawn as a broad bell-shaped curve, with tick marks showing typical mid-sleep times along the axis and the reader’s own position highlightable. A small inset line shows the lifespan trend: chronotype drifting later through adolescence to a peak in the late teens/early twenties, then gradually earlier with age. A schematic informed by population data rather than a decorative image.
What it means for travel
Chronotype gives a moderate but real edge in one direction. As a rule of thumb, evening types (owls) find it a little easier to delay their clock, which favours westward travel, while morning types (larks) find it easier to advance, which favours eastward travel. It is only one factor among several – the number of time zones still dominates – but it is why the jet lag calculator folds your chronotype into the estimate, and why two people on the same trip can adjust at slightly different speeds.
To see how direction interacts with your type, try the eastward vs. westward tool. And remember the baseline: arriving already sleep-deprived from fighting your chronotype at home makes any trip harder, so protect your normal sleep in the days before you fly.
Common questions
Can I change my chronotype?
You can nudge it – consistent early light and earlier sleep push it earlier, for example – but you cannot fully override your genetic and age-driven baseline. Working with your chronotype is easier than fighting it.
How is chronotype measured?
Commonly with questionnaires: the MEQ (preference-based) or the MCTQ (behaviour-based, using mid-sleep on free days). jetlag.info uses a short chronotype question rather than a full questionnaire.
Does my chronotype decide how bad my jet lag is?
It has a moderate effect on which direction is easier for you, but the number of time zones crossed and your light timing matter more. Chronotype fine-tunes the estimate rather than driving it.
Sources
- Horne JA & Östberg O (1976). “A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms.” International Journal of Chronobiology, 4(2). The MEQ.
- Roenneberg T, Wirz-Justice A & Merrow M (2003). “Life between clocks: daily temporal patterns of human chronotypes.” Journal of Biological Rhythms, 18(1). Introduces the MCTQ and mid-sleep on free days.
- Roenneberg T, Kuehnle T, Juda M, et al. (2007). “Epidemiology of the human circadian clock.” Sleep Medicine Reviews, 11(6). Population distribution and age trends.
- Sleep Foundation and NIGMS (NIH) – educational overviews of chronotype.
Measurement tools and population/age patterns are cited from the peer-reviewed sources above; the direction-of-travel effect is a moderate, well-recognised application and is treated as one factor among several.