What is a Micromort?

A visual introduction to everyday risk — then test yourself

How dangerous is your morning?

Every morning involves risk. Brewing coffee. Crossing the road. Commuting to work. Each activity carries a measurable probability of death.

A micromort (mm) is a one-in-a-million chance of death from a single activity.

All of these are below 1 mm — risks so small we never perceive them as dangerous.

The 12x ratio between a 30-minute bicycle commute and a cup of coffee sounds alarming, but in absolute terms it is the difference between a 0.01 and 0.12 in a million chance. Both are negligible.

Hover over the bars to compare.

The full spectrum

Now zoom out. Hover over any dot to see the activity name and micromort value.

The micromort scale spans six orders of magnitude — from a dental X-ray (0.05 mm) to summiting Everest (~38,000 mm).

Bottom (< 1 mm): daily activities — commuting, coffee, office work, dental X-rays. Risks so small we never notice them.

Middle (1–100 mm): risks we weigh consciously — a night in hospital (75 mm), general anaesthesia (10 mm), a long-haul flight (4 mm), running a marathon (7 mm).

Top (> 100 mm): risks that make headlines — base jumping (430 mm per jump), Himalayan mountaineering (12,000 mm), Everest at ~38,000 mm — roughly a 4% chance of death per ascent.

The slow burn

Not all risks kill in an instant.

Some shorten your life by half an hour, every single day. David Spiegelhalter called these microlives (ml) — each one worth 30 minutes of life expectancy.

Smoking 20 cigarettes a day costs 10 microlives. That is 10 × 30 = 300 minutes = 5 hours of life, lost every 24 hours. A heavy smoker lives as though the day were only 19 hours long.

The scale works in reverse too. 150 minutes of weekly exercise gains 3 ml/day. Five servings of fruit and vegetables: +4 ml/day — yes, diet can outweigh exercise in Spiegelhalter’s estimates (both from the BMJ 2012 paper). A Mediterranean diet: +2 ml/day.

Hover over the bars to explore. Red = life lost. Green = life gained.

The bridge

How do you compare a skydive to a cigarette? One kills instantly (rarely). The other kills slowly (certainly, at scale).

The answer is Loss of Life Expectancy (LLE) — the average time lost or gained per exposure.

One micromort costs roughly 21 minutes of life expectancy. One microlife is 30 minutes. So 1 mm ≈ 0.7 ml.

The UK Department for Transport values a micromort at £1.60. NICE values a microlife at £1.70. Two independent government agencies, nearly the same price for a unit of risk.

The three currencies of risk and the exchange rate between them.

Unit	Abbreviation	Definition	Example
Micromort	mm	1-in-a-million death probability	Skydiving (per jump) = 10 mm
Microlife	ml/day	30 min of life expectancy per day	Smoking 2 cigs/day = −1 ml/day
LLE	min	Loss of Life Expectancy	1 mm ≈ 21 min ≈ 0.7 ml
£ value	£	NICE/DfT policy valuation	1 mm ≈ £1.60 ≈ 1 ml/day

Now test yourself

You now have three currencies for risk — micromorts (mm), microlives (ml/day), and loss of life expectancy (LLE).

You know that coffee is 0.01 mm and Everest is ~38,000 mm. You know that smoking costs 10 ml/day and exercise gains 3 ml/day. But how good is your intuition? Three quizzes, three formats:

☠️ Micromort Quiz — which activity is riskier? Pick A or B. Covers acute risks from skydiving to surgery.

⏳ Microlife Quiz — which daily habit has the bigger effect on your lifespan? Smoking vs diet vs exercise.

📊 Rank Risks Quiz — drag and drop 4 items into the correct order. Mixes acute and chronic risks on the same scale.

Ready?

☠️ Micromort Quiz

Which event is more likely to kill you?

⏳ Microlife Quiz

Which daily habit has the bigger effect?

📊 Rank Risks Quiz

Rank 4 risks from biggest to smallest effect.

Session Info

R version 4.5.2 (2025-10-31)
Platform: aarch64-apple-darwin24.6.0
Running under: macOS Tahoe 26.6.2

Matrix products: default
BLAS:   /nix/store/gf17x1bj3m732n39jznn6kz69szbr5rb-blas-3/lib/libblas.dylib
LAPACK: /nix/store/5kg4z5bffhr8nry8bl8l5wlxvpy54dm2-openblas-0.3.30/lib/libopenblasp-r0.3.30.dylib;  LAPACK version 3.12.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: Europe/Belfast
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] plotly_4.11.0   dplyr_1.1.4     ggplot2_4.0.1   micromort_0.2.0
[5] testthat_3.3.1

loaded via a namespace (and not attached):
 [1] gtable_0.3.6       bslib_0.9.0        xfun_0.55          htmlwidgets_1.6.4
 [5] processx_3.8.6     callr_3.7.6        crosstalk_1.2.2    ps_1.9.1
 [9] vctrs_0.6.5        tools_4.5.2        generics_0.1.4     base64url_1.4
[13] tibble_3.3.0       pkgconfig_2.0.3    secretbase_1.0.5   data.table_1.18.0
[17] checkmate_2.3.3    RColorBrewer_1.1-3 S7_0.2.1           desc_1.4.3
[21] assertthat_0.2.1   lifecycle_1.0.4    compiler_4.5.2     farver_2.1.2
[25] credentials_2.0.3  brio_1.1.5         codetools_0.2-20   sass_0.4.10
[29] htmltools_0.5.9    sys_3.4.3          usethis_3.2.1      yaml_2.3.12
[33] lazyeval_0.2.2     jquerylib_0.1.4    pillar_1.11.1      tidyr_1.3.2
[37] DT_0.34.0          openssl_2.3.4      cachem_1.1.0       tidyselect_1.2.1
[41] digest_0.6.39      purrr_1.2.0        arrow_22.0.0       rprojroot_2.1.1
[45] fastmap_1.2.0      grid_4.5.2         cli_3.6.5          magrittr_2.0.4
[49] pkgbuild_1.4.8     withr_3.0.2        prettyunits_1.2.0  scales_1.4.0
[53] backports_1.5.0    bit64_4.6.0-1      rmarkdown_2.30     httr_1.4.7
[57] igraph_2.2.1       bit_4.6.0          otel_0.2.0         askpass_1.2.1
[61] evaluate_1.0.5     knitr_1.51         viridisLite_0.4.2  rlang_1.1.6
[65] gert_2.2.0         Rcpp_1.1.0         glue_1.8.0         pkgload_1.4.1
[69] jsonlite_2.0.0     R6_2.6.1           targets_1.11.4     fs_1.6.6
[73] units_1.0-0       

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micromort 0.1.0 | Git 94d93d2 | R 4.5.2 | Built 2026-04-18 12:20:56