My wife and I retired at age 55 around 8 years ago. Like you, we had a good household income and lived well below our means but had no formal budget. About a year prior to retirement, I started mapping out where we spent our money. Kind of like reverse engineering a budget. Then I altered this budget based on what I thought our retirement would look like. So I changed allocations for things like travel and health care. Once we pulled the trigger and retired, I monitored our actual spending and compared it to our budget on a monthly basis. I think I did this for the first two years. I changed the allocations for each budget category based on actual spending but our total annual spend was very close to our budget. After a while, we got more comfortable with our ability to match our spending with our budget and now we only check our spending at the end of the year. Even though we no longer consciously monitor our spending, we always hit our budget right on the nose when we check at the end of the year.