How does clearblue digital calculate dates

[MoonstoneGoddess]

Just out of curiosity.
Clearblue says 3+
So how exactly does it calculate this ?
I should be 6 weeks pregnant according to dates.
Clearblue calculates the actual date of conception. Do you add any weeks onto this ?
The way nhs count 4 weeks when period is due except for we know 2 of those your not actually pregnant but it's still counted.
If clearblue said 3+ yesterday and I'm 6 weeks does this mean my baby is measuring behind ? I had ivf so know my trasnfer date

To my knowledge Clearblue doesn't go any higher than 3+, so it literally means that, it thinks from your hcg level that you are more than 3 weeks pregnant. If you know your transfer date then you can calculate your due date from there, and it'll be confirmed at a dating scan.