Budgets tend to be dropped within weeks, because a budget is a plan for money you haven't looked at yet. It works better in the other order: look at what you actually spent first, then plan.
Your first day
Guess first, then look. Before opening anything, write down how much you think you spent last month on four things: fixed bills such as rent and phone, food, subscriptions and automatic charges, and everything else.
Then open last month's bank and card statements, in the app or as a downloaded file, and go through every line. Mark each one with one of those four labels and add up each group. Expect the first pass to take up to an hour. A wrong label doesn't matter, so pick one and move on.
Compare each total with your guess. The gap is often largest in subscriptions and automatic charges, because those are payments you never decided on this month. You're done when you have four totals and four guesses side by side.
The thing most people miss
The point isn't the budget, it's the gap between your guess and the total. People tend to remember big, occasional purchases like a night out or a flight, and forget small ones that repeat, because an automatic charge never feels like a decision. Surveys of consumers have found they underestimate their subscription spending by a wide margin.
That gap is more useful than a spending limit. It shows which of your assumptions about money are wrong, and the fix is often a single cancellation rather than a change in how you live.
What not to buy
Don't pay for a budgeting app or template yet. A pen, a spreadsheet or the notes on your phone handle four totals fine, and an app is easier to choose once you know which numbers you'd want it to track.
The next step is to act on one line: cancel a charge you don't use, or call to lower a bill. Then repeat the same four-part count next month and compare the totals. Two months of real numbers tell you more than any budget template could.