Has anyone actually used a teacher pay calculator that gets it right?

I’ve been trying to work out my actual take home pay for next year and I keep getting different numbers depending on where I look, which is driving me a bit mad. I’m on M4 in the Rest of England and with the 3.5% uplift confirmed I should be somewhere around £40,941 gross, but when I try to work out what actually lands in my bank each month I keep coming unstuck on the pension. The tier thing confuses me because I’ve read that crossing a boundary means the higher rate applies to your whole salary, not just the bit above the threshold, and I’m fairly sure I’m close to one of those lines but I can’t work out which side I fall on. I’ve tried doing it manually with the HMRC figures but I’m not confident I’ve got the order right, because tax comes off after pension but National Insurance doesn’t, and student loan is calculated on gross which is yet another different starting point. Someone in the staffroom mentioned a teacher pay calculator that supposedly does all of this properly including the pension tiers and the regional differences, and I had a look but I want to know if anyone here has actually used one and found it accurate, because I’d rather not make decisions about whether I can afford to go down to four days a week based on figures that turn out to be wrong. I’m also curious whether these calculators handle the part time pro rata correctly, because that’s the bit that really matters for me, and whether they account for the fact that your pension rate is based on your actual part time salary rather than your full time equivalent. If anyone has used one and compared it against their real payslip, I’d really appreciate hearing how close it was, because I’m trying to plan properly for next year and I don’t want any nasty surprises.