I cannot really put a figure on it as the income varies..
But I do it this way..
On the 24th of each month I work out the VAT (19% here) put that into the tax account.
Then housekeeping money of x amount is transferred to g/f account.
Then the amount needed to run the business i.e fuel, insurances vech taxes etc whatever is transferred to 'running' acc.
Then with what ever remains is broken up into 70%/30%...70% into savings and 30% into Tax account.