Start with your monthly take-home income, then list fixed costs such as rent, council tax, utilities, broadband and regular debt payments. Add changeable spending, including travel, food, childcare and entertainment, using recent bank statements to set realistic London figures rather than guesses. Build in irregular costs, such as annual insurance, repairs and season-ticket payments, by dividing them into monthly amounts, and keep a small emergency buffer if possible. You can check council tax details on GOV.UK and compare your plan with free budgeting tools from MoneyHelper, adjusting it each month as your circumstances change.