but how soon after dtd would you get a blue line
Im not an expert on this but I think the blue line is not related so much to when you dtd as much as when your AF is due. According to the clearblue website you can test as early as 5 days before your AF. So if your AF is due on the 31st of Jan and you dtd on the 5th of Jan the earliest you can test is the 26th of Jan, likewise if you dtd on the 20th of Jan the earliest you can test is still the 26th of Jan. All that said I did a test 5 days before my AF and it was a BFN and it was only when I missed my AF that I got a BFP (maybe if Id tested 3 days before I might have gotten a bfp, I left it a week so it was 2 days after AF was due).
I hope this was helpful, sorry if I misunderstood your question.
little mrs sunshine
Your response has given me a small bit of hope.
AF was due Saturday but never came so I tested Sunday and it was BFN. Still hasn't arrived so if it doesn't come today testing tomorrow and keeping everything crossed and praying I get my BFP
It depends which test you use Peaseblossom.
The two I used were Clear Blue (regular), which says it's accurate from the day AF is due (got a faint positive the day before) and First Response, which says it may be accurate up to 4 days before (got v. faint positive 3 days before).
Haven't used ClearBlue digital but it is probably the one that is accurate 5 days before.
If you read the First REsponse leaflet though, it specifies that it was accurate 4 days before AF in 69% of women only in tests - this figure goes up to 99% on day AF is due.
So you're better to wait until AF is due or late - if you have the self control that is (I don't!)