This caveat on the European Union - EES / ETIAS calculator is super-important:
Please note that the remaining authorised stay does NOT reflect any time spent in the Schengen area that began before 10 April 2026, regardless of whether the visit ended before or continued after that date.
I tried it for my upcoming flight on 14-May: it said “Remaining days at the moment of entry: 72” when the correct answer is actually 8 
…so it counted my 18 days in the EU in April, but not my 17 days in March or anything before then.
PS. Just checked my spouse’s passport: calculator has their 2 days in Spain since 10-April, but is missing another 19 EU days after that!