In one sentence
The three profile facts most calculations need: your date of birth, from which VT takes your age on the day; your sex, which picks the reference population and the formula; and your height, which turns weight into a body mass index, a waist into a waist-to-height ratio and a scale's pulse transit time into a pulse wave velocity.
Why it matters
Almost every reference VT reads a number against was built by age and sex, and most formulas carry height. Energy expenditure adjusted for body composition is stable from 20 to 60 and then falls by about 0.7 percent a year, in 6,421 doubly-labeled-water measurements across the life course (Pontzer 2021), which is why age sits in the energy formulas and why the fall is gentle. Fitness is judged against people of the same age and sex, because a VO₂ max that is elite at 60 is average at 25 (Mandsager 2018). The body-fat reference medians differ by more than ten points between men and women at every age (Kelly 2009). The pressure indices begin at 50 because that is where the Framingham analysis found the information shifting from diastolic to pulse pressure (Franklin 2001). Metabolic age, PhenoAge, the kidney estimate and free testosterone are all sex-specific equations, and the sleep score's duration bands are age-banded. The table says what needs what.
| Calculation | Date of birth | Sex | Height | | --- | --- | --- | --- | | Vitality Score (the headline) | Yes | Yes | Yes | | Energy expenditure formulas | Yes | Yes | Yes | | Metabolic age | Yes | Yes | Yes | | Body-fat percentile | Yes | Yes | — | | Pulse pressure, MAP and fractional pulse pressure | Yes, from 50 | — | — | | Pulse wave velocity from a scale | — | — | Yes | | Body mass index, waist-to-height ratio, fat-free mass index, ideal weight range, maximum muscular potential | — | Yes, for the ranges | Yes | | Sleep duration band, VO₂ max norms, maximum heart rate | Yes | Yes, for the norms | — | | eGFR, PhenoAge, free testosterone, hepatic steatosis index | Yes | Yes | — |
What to enter
The date of birth, once. For sex, VT asks for the category the reference populations and formulas were built on, male or female, because every one of them was; the app needs it to finish setup; if it is left blank on the web, metabolic age shows the average of the two results, and sex-specific figures such as VT's vascular age and the body-fat percentile are not shown. Height measured once, properly: shoes off, heels against a wall, head level, and in the morning, since you are about a centimeter taller then than in the evening; re-measure it every few years after 50, because height falls slowly through later life and a stale height overstates the waist-to-height ratio.
How Vitality Tracker uses it
As the table shows, and nowhere else: age changes how a result is framed only where a published reference is age-banded (fitness is scored for ages 20 to 79, metabolic age for 18 to 100) and in the rule that starts the pressure indices' direction at 50, and no entry on this site addresses you by your age. The three facts head the pre-visit report, and when you correct your height, VT recalculates metabolic age for every past day with the new height.
How far to trust the number
Self-reported, and the error is in height: two centimeters moves the body mass index by about 0.7 and the waist-to-height ratio by about 0.006, which is a few tenths of a year of metabolic age and a step in the body-composition area. Measure it once well and the rest is arithmetic.
Sources
- Pontzer H, et al. Daily energy expenditure through the human life course. Science 2021;373:808–12. doi:10.1126/science.abe5017
- Mandsager K, et al. JAMA Netw Open 2018;1:e183605. doi:10.1001/jamanetworkopen.2018.3605
- Kelly TL, Wilson KE, Heymsfield SB. PLoS One 2009;4:e7038. doi:10.1371/journal.pone.0007038
- Franklin SS, et al. Circulation 2001;103:1245–9. doi:10.1161/01.cir.103.9.1245
- Vitality Tracker, the engine catalogue of 15 October 2026 (the profile record and what it feeds).