Hi all, I could really use some advice as I'm getting really confused over sick pay and maternity pay calculations.
I'm 20+3 weeks pregnant, and I've been signed off work for the duration of my pregnancy due to HG and other high risk complications. My work have been really good about it, and we have a very generous sick pay policy of 6 months on full pay and then 6 months on half pay.
The way it will work (that I've agreed with our HR) is that I will go straight from being off sick but on full pay to being on maternity leave.
The thing I'm confused about it will this affect my SMP? When do they do the SMP calculations? I've read a lot about how if you're on SSP it will lower your average earnings, and so you will have lower SMP, but does this work the same way if you're off work on full pay, and not on SSP? 
Lastly, when do you need to hand your MAT1B form in to your employer? I thought it was before 25 weeks but the midwife said before 28 weeks, and apparently she'll give it to me at my next appointment, which is as 26 weeks. I was wondering whether I should make an appointment for 24 weeks and just get it then.
If anyone could shed any light on these I'd be very grateful thanks.