All a guessing game really, doesn't really matter much, baby comes when baby wants
I kept dates when I got pregnant with my son, sperm can live up to 3 days inside the vagina.after trying for a year and a half, I calculated my due date to be december 13th at the latest and the dr calculated my due date to be dec 20th. I started having labor contractions on dec 15th but since my contractions "weren't strong enough" but were coming every 3 min. They sent me home and I ended up having to be induced on dec 30th and found out my son cooked too long as he pooped inside me and came out via emergency csection weighing 9lb 4oz. So it's definitely possible their date could be off
If you are due May 20, your midwife has calculated your conception date to be around August 27. Since you're now 24 weeks, if you just now got an estimated due date it's possible it could be off by several days.
What did she use to calculate your due date?
Based on my last period my due date would have been 24th March, scan at 12 weeks said 28th March, then subsequent scans have come out with the 22nd March and 24th lol its all rough guesswork :) congratulations on your pregnancy
Honestly, due dates are a bit of a guess for all involved. As sperm lives for days it's just hard to say. Very very few women have their babiesON their actual due date.