Wrong date calculation?

[Moonbase59]

I’m showing "current age in years" in my people notes, but the calculation result is wrong: It shows a wrong age.

Today is 2021-05-04, and the person’s birthday is 1997-05-17, so she is clearly 23 years of age and about to turn 24 on May 17.

I have in the front matter:

---
birthday: 1997-05-17
---

and I use

`= (date(today) - this.birthday).years + " Jahre"`

to calculate. The result is 24 Jahre (instead of 23 Jahre).

In order to verify, I put

`= (date(today) - this.birthday)`

which results in 24 years (instead of 23 years, and something).

Clearly a bug, I feel. Does this calculation "round" somehow? And if yes, can that be turned off to get exact results?

---

I have another table that shall show "upcoming birthdays in the next 2 months", with 3 columns File, Birthday, and Turns. This also shows that she’ll be turning 25 instead of 24.
Here’s the code:

table birthday as "Birthday", choice(
date(today).month*100+date(today).day = birthday.month*100+birthday.day,(date(today)-birthday).year,(date(today)-birthday).year+1) as Turns
from "People/Friends & Family"
where file.name != this.file.name and
choice(date(today).month*100+date(today).day > birthday.month*100+birthday.day,
(date(today).year+1)*10000 + birthday.month*100 + birthday.day,
date(today).year*10000 + birthday.month*100 + birthday.day) <= (date(today) + dur(2 months)).year*10000+(date(today) + dur(2 months)).month*100+(date(today) + dur(2 months)).day
sort choice(
date(today).month*100+date(today).day > birthday.month*100+birthday.day,
(date(today).year+1)*10000 + birthday.month*100 + birthday.day,
date(today).year*10000 + birthday.month*100 + birthday.day)

so I assume dataview really returns a "bad" (or rounded?) calculation result!

I’m (wildly) assuming you’re using some “forum-like-date-display” code here, where it might be okay to say “someone commented roughly 24 years ago” but I would prefer exact results when working with a database-like system. Otherwise we won’t get good and exact birthday-type calculations, right? 😉

Hint: If using moment.js, relative time thresholds can be customized: https://momentjs.com/docs/#/customization/relative-time-threshold/

[blacksmithgu]

Apparently luxon rounds date differences internally (for what reason, I have no idea); I've updated date subtraction to produce exact durations.

[Moonbase59]

It’s probably for forum use, like in moment.js: The longer a datediff is, the less exact it is shown, i.e. not

3 years, 11 months, 30 days, 17 hours, 18 minutes ago

but

4 years ago

if its (I think) > 320 days into the year or so.