Of course, there's no avoiding this time-consuming step of writing a budget. Though you may consider yourself financially savvy, chances are you can't keep all the necessary details in your head. It'll help to actually sit down and track your money.
You'll need to record your income and expenses over the past few months. To get an accurate assessment, gather your bank statements, paycheck stubs and bills. If you use online banking, this might only require logging in to see exactly how much money comes and goes. Ideally, start collecting your detailed receipts ahead of time. The more detailed you're able to get, the better you'll be able to assess where your money goes.
Income for salaried workers is steady and easy to record and predict. But others who work hourly or whose income fluctuates will have to take more general estimates and plan for changes in their budget from month to month. Likewise, expenses can be fixed and always the same amount (like a monthly Internet bill), or unfixed and fluctuate based on the season or month (like energy and gas bills, or groceries).
Finally, categorize and sum up both your income and expenses on a monthly basis. This will allow you to visualize your monthly financial activity easily.