Include all variable expenses now, car maintenance, electricity, heating, these can vary throughout the year you need to calculate them and come up with an average monthly amount. None essential expenses like eating out coffee at Starbucks, weekend getaways, extravagant vacations, fancy clothing, motorcycles, ATV's, if you use them, write them down, realize these are wants, not needs. Now total these all up, fixed expenses, variable expenses, and non_essential expenses,there you now have your total expenses.
Cut out. Lots of us pay for things we do not even use. This is another mistake that gets easier to make with so many automated payment plans. Do you keep a gym membership that you do not use? Replace that with a brisk walk, weights, or a stationary bike. You will not have to make monthly payments, and you may find it is more convenient.