I’ll have a go at another explanation, rather than a diagram
Bank holidays are pro rated. You get 4/5 of a bank holiday as your bank holiday leave, and the other 1/5 comes out of your normal holiday allowance.
in practice your employer:
- adds the bank holidays to the paid annual leave to get the total number of paid days off you’d get if you were full time
- divides that total by your working pattern (in your case 80%)
- deducts any bank holidays that fall on your working days from that
- you get the balance as paid leave you can take when you want
Let’s assume annual leave entitlement if you’re full time is 20 days + 8 days bank holiday = 28 days total
You are entitled to 4/5th or 80% of that = 22.4 days (your employer may round this up to 25, but they don’t have to).
In 2024 there are 8 bank holidays . 5 fall on a Monday. 1 falls on a Friday
If you don’t normally work Mondays, only 3 bank holidays fall on your working days. They deduct those 3 days from your 22.4 days total pro rated paid leave. You are left with 19.4 days to take when you like.
If you don’t normally work Fridays, 7 bank holidays fall on your working days. They deduct those 7 days from your 22.4 days total pro rated paid leave. You are left with 15.4 days to take when you like.
In both scenarios you get the same total number of days off. But if you don’t work Mondays you get more choice of when you take them.