Start with your monthly take-home income, then check your bank statements and list essential spending such as rent, energy, food and travel. Add regular but less frequent costs, such as insurance, car repairs and Christmas, and divide their yearly total by 12 so you can set money aside each month. Subtract your spending from your income and give any remainder a job, such as building emergency savings or reducing expensive debt. Review the budget after a month and adjust it using your actual spending; a notes app, spreadsheet or budgeting app can help.