If you are spending a massive £80 + on birthdays, then that definitely needs to be in your budget to begin with.
As well as the normal monthly bills (utilities, phones, Water, Council tax, insurances) and you petrol, other travel, food, etc. You need to add up what you spend over the year, on irregular or annual things such as
Car repairs
Car depreciation
Car Tax
Car Ins
TV Licence
Boiler service etc.etc.
then:
presents (birthday / Christmas / collections at work / weddings etc)
clothes
hair / makeup / treatments
holidays
'Going out' - be that a meal with dh or with friends or family treat days out or cinema
Other 'treats' you like
then 'long term savings'
and 'emergency fund savings' - replacing a fridge or oven
then 'maintaining the property' costs .... decrating a room each year, plus saving for that day when you need roof repairs or the boiler needs replacing.
Add up the year's total, add on 15 - 20% for what you forgot, then divide by 12.