Hi
I am not sure there is any way of us knowing how they calculate these things. I have been on TC since 2014 and though I thought I had nailed their calculations, I never have.
I think they base it on the previous years earnings unless you will be earning £2500 lower or £2500 higher, then they will base your award on your estimated earnings for the current tax year.
Anyway, I cant make any promises but if your tax credits were based on £26,000 and you earn't less then there shouldn't be any overpayment. Have you run it through the online calculator to give you a rough idea. I know they aren't accurate, but it will give a little indication.
But in reality, no one knows how they work things. I've mostly been told ive been overpaid despite me never being able to work out how and where.
The renewal is the only way you will know. And a word of advise, keep a copy of the letter where it basically closes off your previous tax year with their final award decision.
I used to read absolute horror stories of how they approached people 10 years on chasing overpayments that were only just being brought to their attention. That made me literally sift through years of paperwork and order them by date and any I didn't have I requested copies of.
Now I know if they ever say to me you were overpaid in 2014 for example, I have their written proof that the renewal process was closed and what their final award notice was.
I hope this makes sense xx