Quote (from the Gov.uk website):
"How much income you get each year from an annuity depends on things like:
how much you had in your pension pot when you bought the annuity
your age
whether you want the income to increase each year
whether you want the annuity to pay out to someone after you die
your health and lifestyle
You may have to pay administration fees"
Source:
https://www.pensionwise.gov.uk/en/guaranteed-income#how-an-annuity-is-calculated
There's a basic calculator provided on that Gov.uk page. For a more detailed one, try this:
https://www.aviva.co.uk/pac/