It can be challenging to estimate your monthly budget in retirement, as many of your expenses will change. For instance, you might no longer have a mortgage payment, but you may take on new health care expenses that your employer previously covered. Your tax situation could change based on your new income totals, too. You may also plan to travel more often. It's a good idea to spend some time considering every expense that could change in retirement (including cost-of-living expenses if you plan to move) and plan ahead.