Most budgets fail in the first month. Not because of maths, but because they're built the wrong way. A budget that works describes how you actually spend, then gradually shapes it. One that doesn't lists aspirational figures and collapses the first time something unexpected appears.
Before setting any targets, look at three months of bank and credit card statements. Add up what you spent in each category. The numbers will probably surprise you. Most people underestimate food and eating out by around 40%. Most people forget at least two or three subscriptions. Most people have never added up what they spend on clothes in a year.
Once you know where the money went, you're working with reality rather than wishful thinking.
The 50/30/20 rule splits your take-home pay into needs (50%), wants (30%) and savings (20%). It's a useful benchmark rather than a rigid rule. If your rent takes 40% of income on its own, the percentages need adjusting to fit your life.
Zero-based budgeting assigns every pound a job before the month begins. It takes more effort but leaves nothing unaccounted for. Pay-yourself-first treats savings as the first outgoing, not what's left at the end — automate the transfer on payday and budget with what remains.
Spend less than you earn. Everything else is a system for making that easier.
Every budget needs a miscellaneous category. Life produces small unexpected costs constantly. A budget with no room for them creates the feeling of failing constantly, which leads to abandoning the system entirely.
Review it monthly, not daily. Daily checking turns into obsession. Monthly checking spots patterns and lets you adjust.