I'm trying to create a pension prediction spreadsheet for myself. One of the input variables is going to be the pension withdrawal rate. Looking around the web, I can see that typically folks are recommend to make this in the 3-4% range; for example, Investopedia recommends that. This generally seems to just be a fixed number which doesn't vary according to any other criteria.
However, surely the withdrawal rate should depend on the age at which I retire (which is also an input to my spreadsheet). If I retire early (e.g. 55 rather than the "standard"/state retirement age where I live - the UK - which is 68), shouldn't the withdrawal rate be quite a bit lower to avoid running out of money?
Should I / how can I calculate an appropriate withdrawal rate? If there a standard formula I can use? I've searched the web quite a bit, but I can't find anything appropriate which isn't completely impenetrable except for dyed-in-the-wool professionals.