Overtime hours

I recently had a problem with my housing benefit after doing some overtime. I just want to know how many hours overtime I can work without it effecting my housing benefit? And if I do more than that what would I then receive in HSA? Trying to find out if I'm able to do overtime and still be better off. I tried using benefit calculator but I'm not sure what I did wrong as it says the same no matter how many hours I entered. I get £8.10,an hour. Please help.