Frequent-flyer dose math: when it actually starts to matter

The arithmetic is roughly linear in flight hours, so the crossovers with the ICRP-103 and FAA reference numbers are easy to find on a napkin. Two second-order effects nudge the numbers (cruise altitude and geomagnetic latitude), but the polar and altitude guides handle those in depth. What follows is the napkin math with the sources attached.

The baseline dose rate

The clearest anchor is a transatlantic segment. At the July 2026 solar-cycle phase our CARI-7 engine puts JFK-LHR at 4.2 µSv per flight hour, which is why 1 mSv takes about 240 hours of transatlantic flying ^[1]. Domestic and low-latitude flying runs lower. Engine route averages:

Route type	Typical in-flight dose rate (µSv/hr)
Short-haul domestic US (LAX-PHX, FL310)	1.4
Caribbean / Pacific short long-haul (JFK-SJU, LAX-HNL, FL370)	1.9–2.4
Transcontinental US (JFK-SFO, FL370)	3.4
Transatlantic (JFK-LHR, ORD-LHR, DFW-LHR, FL390)	4.2–4.3
Transpolar (JFK-NRT, YVR-LHR, JFK-HKG, FL390–FL400)	4.1–4.4
Low-latitude long-haul (SIN-SYD, LHR-SIN)	2.1–2.7

For the rest of this guide we use 4.2 µSv/hr, the transatlantic rate. A domestic-heavy pattern runs roughly 20% below that; a pattern built on low-latitude long-haul runs closer to half.

The annual dose ladder

Annual flight hours, multiplied by 4.2 µSv/hr, gives annual flight dose. Set against reference values:

Annual flight hours	Equivalent flying volume	Annual flight dose (mSv)	Where this sits
10	~ 1 transatlantic round trip	0.04	Rounding error on background
25	~ 2 transatlantic round trips	0.11	1.7% of the 6.2 mSv/yr US average including medical
50	Light business travel: fortnightly domestic + 1 international/yr	0.21	~ 64% of the 0.33 mSv/yr ground-level cosmic dose
100	Active business travel: bi-monthly transatlantic + weekly domestic	0.42	42% of the ICRP public 1 mSv
200	Heavy business travel: monthly transatlantic + weekly domestic, all year	0.84	Approaches ICRP-103 public 1 mSv, which arrives at about 240 hours
400	Very heavy: biweekly transatlantic, near-constant US domestic	1.7	1.7x ICRP public; ~ 28% of the 6 mSv EURATOM level
600	Lower bound of short-haul cabin-crew hours	2.5	42% of the 6 mSv EURATOM level
800	Typical long-haul aircrew	3.4	56% of the 6 mSv EURATOM level
1,200	Hard ceiling on FAA Part 121 line aircrew (14 CFR 121.471 caps duty/flight time, not flight time alone, but ~1,000 hr/yr is a practical maximum)	5.0	Just under the 6 mSv EURATOM level

(For 14 CFR 121.471, flight-time limitations on US Part 121 carriers, see the eCFR reference ^[2].)

What each reference number actually means

• US per-capita exposure including medical, 6.2 mSv/yr. NCRP Report 160 (2009) puts the total at about 6.2 mSv/yr, of which roughly half is medical. The natural-background half is about 3.1 mSv/yr ^[3].
• Cosmic component of US background, 0.33 mSv/yr. The ground-level cosmic-radiation contribution at the US per-capita altitude.
• ICRP public limit, 1 mSv/yr. Reference for additional dose from controllable sources; cosmic is technically excluded, but the figure is the most familiar benchmark. ICRP-103 ^[4].
• EURATOM roster-management level, 6 mSv/yr. Article 35(3) of Directive 2013/59/Euratom. Above it, an EU operator must take assessed exposure into account in organizing schedules. FAA AC 120-61B contains no 6 mSv figure; it recommends 20 mSv/yr averaged over five years, 50 mSv in any one year, and 0.5 mSv per month once a pregnancy is known ^[5].
• ICRP occupational limit, 20 mSv/yr (averaged over 5 years). Enforced for radiation workers under EU EURATOM rules; recommended elsewhere ^[4].

A polar-heavy pattern runs about 30% above a domestic one

The gap is between latitudes, not between the polar routes and the transatlantic baseline. JFK-SFO averages 3.4 µSv/hr; JFK-NRT and YVR-LHR average 4.3 and 4.4. So swapping a transcontinental pattern for a transpolar one raises the rate by roughly 30%. Going the other way is a bigger move: SIN-SYD averages 2.1 µSv/hr, half the transatlantic rate.

What this does not tell you

• It does not tell you individual cancer risk. The translation of mSv to lifetime attributable risk depends on BEIR VII coefficients ^[6] applied to a population, not to an individual.
• It does not include solar-particle-event variation (see our SPE guide).
• It does not adjust for individual radiosensitivity factors (age at first exposure, sex, prior medical radiation history).

Where fliers actually land on this chart

Most non-occupational fliers sit well below the ICRP public 1 mSv reference and near the cosmic component of natural background. Heavy business travel crosses the public reference but stays well under 6 mSv. Only the heaviest long-haul aircrew patterns approach the 6 mSv EURATOM level, and even those remain far below the 20 mSv occupational limit. Two levers reduce annual dose in practice: fewer hours, and fewer polar hours specifically. Aircraft type, seat selection and window vs aisle do not.

What a real year of trips comes to

Rather than hours, it is often easier to count trips. Two worked examples straight from the engine, at the July 2026 solar phase:

Flying pattern	Annual dose
10 JFK-SFO round trips, 3 LAX-LHR round trips, 1 LHR-SIN round trip	0.68 mSv
10 polar transatlantic round trips	0.89 mSv

The first pattern is 23 percent of the 3.1 mSv/yr US natural background. Neither reaches the 1 mSv ICRP public reference, and ten polar transatlantic round trips a year is a heavier schedule than most business travelers keep.

The career-cumulative picture

For long-term planning, the annual figure matters less than the career cumulative. Holding a pattern constant at 4.2 µSv/hr over thirty years:

• Light business travel (50 hr/yr): about 6 mSv of additional cosmic dose from flying.
• Heavy business travel (200 hr/yr): about 25 mSv.
• Long-haul aircrew (800 hr/yr): about 100 mSv.

A career total in the 100 mSv range is where the BEIR VII risk coefficients start to give a lifetime attributable risk increment that is small but not negligible against the background lifetime cancer mortality of roughly 23% for a typical adult ^[6]. It is also the regime in which the flight-attendant cohort studies start to detect cancer-incidence elevations (see our flight attendants and cancer guide). The report gives you a per-year figure, not a career projection; multiplying it out is your call, not something we print.

Two common mistakes in mental arithmetic

• Confusing flight hours with travel hours. Block time (gate to gate) is roughly 30–60 minutes longer than airborne time on most flights, and only airborne time accumulates cosmic dose. We use airborne time in the math above.
• Forgetting climb / descent. Climb and descent contribute meaningful dose for short-haul flying but are a small share of long-haul. The report models a climb, cruise and descent profile explicitly rather than applying the cruise rate across the whole block time, so the lower dose rate during those phases is already accounted for.

How dose compares to natural background year-on-year

One useful frame: how many days of ordinary US exposure does a year of flying equal? Measured against the 6.2 mSv/yr US per-capita total including medical (NCRP 160), at 4.2 µSv/hr:

• For a flier doing 50 hr/yr, one year of flying equals about 12 days.
• For a flier doing 200 hr/yr, one year of flying equals about 49 days.
• For a long-haul aircrew member doing 800 hr/yr, one year of flying equals about 198 days: over half a year, but still less than one annual per-capita dose.

None of these patterns delivers dose that is large in absolute terms. The case for paying attention to flight dose is not that the numbers are alarming; it is that they are non-trivial for the heaviest patterns and that flight dose is one of the few dose sources adults can actively modulate in their own behavior.

Why "average" matters less than "consistency"

Two fliers with identical 200 hr/yr averages can have very different dose profiles. Flier A does a steady 4 transatlantic round-trips per month. Flier B does no flying for nine months and then a five-week intensive trip block. Their annual doses are equal in expectation, but flier B's dose is concentrated. From a stochastic-risk perspective both are equivalent under the LNT model; from a practical health-decision perspective, neither pattern triggers a meaningful difference. The numbers are simply useful for understanding what your total exposure is and how it compares.

Reviewed 4 September 2026 · See our methodology and sources.