I have a spreadsheet in which I record every financial transaction, and enter all future transactions, estimated as necessary, out to a year ahead. Whenever I get a bank statement, credit card statement, or the like, I compare everything in it with the spreadsheet and correct things as necessary. I don't try to keep track of cash spent out of my pocket. I tried that once, but found it wasn't practical. The numbers would never add up and there would be no independent record to check them against.

One row of the spreadsheet computes my total financial assets, which I observe ticking upwards month by month.

I don't record in detail what I buy, only the money spent and where (which is a partial clue to what I bought). I'm sufficiently well off that I don't need to plan any of my expenditure in detail, only consider from time to time whether I want to direct X amount of my resources in the way I observe myself doing.

I spend less than I earn, because it seems to me that that is simply what one does, if one can, in a sensibly ordered life.