Methodology
How the counting works.
The arithmetic nobody does on purpose, done carefully, with its assumptions in plain sight.
The data
Every estimate begins with the United States Social Security Administration's period life tables for 2022, the most recent complete set. A period table answers a narrow question: at a given age, how many more years does an average person of that sex live, if mortality stays exactly as measured that year? The page embeds seventeen anchor ages per sex and interpolates linearly between them. Relations that name a sex use the matching table. Old friends use the sex-averaged one. The values cross-check against the CDC's final 2022 figures: 80.2 years at birth for women, 74.5 for men.
We chose period tables over cohort tables deliberately. Cohort tables project future improvements in mortality, which would grant nearly everyone a little more time, and would also hand us forecasts to defend. The page uses the table that is measured, not projected. Mortality in 2022 still carried some pandemic elevation, so if anything the counting slightly understates your time.
You both have to be there
A visit requires two living people. The horizon is therefore capped at the smaller of two numbers: their remaining expectancy and yours. This joint horizon is why a young parent's card reads differently from an old friend's.
One honest caveat. The true expected length of a joint lifetime is slightly shorter than the smaller of the two expectancies, because either of you could be the one the average misses. Computing that exactly requires full survival curves rather than interpolated anchors, and the difference is small next to the uncertainty in any single life. We accept the simplification, and record it here rather than hide it.
The count
The what-if dial on every card is this same formula at a different cadence. Nothing else moves. That is the page's whole argument: the actuarial half of the equation is fixed, and the cadence half is entirely yours.
The past, and the parental exception
For most relations, time already spent is priced at your declared cadence: years known, times visits per year. One unit for both directions of time.
Parents are different. We borrow the insight from Tim Urban's The Tail End: if you left home around eighteen, the great majority of your time with your parents was already spent by then, at close to daily density. So for mothers and fathers, the first eighteen years are counted at about 330 times a year, and every adult year at your declared cadence. That is why a parent's verdict often says you have used 99 percent of your times together, and why it adds that most of them came before you turned 18. The number is hard. As far as we can tell, it is also true.
A worked example
Your mother is 68. You are 38. You see her a few times a year, which the page counts as four.
remaining ≈ 17.6 × 4 ≈ 70 more times
childhood: 18 × 330 = 5,940 · adulthood: 20 × 4 = 80 · spent ≈ 6,020
6,020 of 6,090 ≈ 99% already used
What this is not
It is not a prediction. Real lives are not averages. Someone you love may far outlive every table, and none of us is promised the average. The uncertainty is not a flaw in the arithmetic. It is the argument for going this weekend.
It is also not surveillance. The math runs entirely in your browser. Names and ages are never sent to a server. The link the page writes after the # stays on your device until you choose to share it.
Corrections and better sources are welcome. The page will always say what it assumes.