Realistic Budget in London?

This has been answered about a billion times on this sub but here we go again.

Monthly post-tax income is ~£4100

Work backwards from essentials: shelter (rent/bills), food, commute, and saving and then think about everything else. Personally I'd start with a savings goal/goals because that anchors your budget. This includes home/retirement and excludes holidays for now. How much is it, when do you want it by. If your savings goal is too ambitious, the rest of your budget will look "too small". You'll see. Personally this is about £1500 for long term investments + £250 to house deposit + £400 to pension. That £400 to pension works out at  ~7% contribution pre-tax so that actually turns your post tax income to ~£3900. Minus £1750 is £2150.

Then food is probably a flat £300. You could easily spend less but given we're in finance, you're not going to probably. £1850.

Bills are probably ~150-200 a month if you're sharing. That's utilities, council tax, internet, maybe even subscriptions (depends how many sharers). £1650.

Commute is ~120 a month I reckon but that could be lower. £1530.

Then you could put like £300 to misc/holidays.

And £1200 on rent.

This is all excluding any bonus you get. So if you think any part of this (e.g. misc/holidays) looks small, you can just pay for it (or accrue it) out of your bonus. Assuming you get at least 5k, that'll cover anything else. Otherwise just save less.