For the last 4 years, I have been regularly calculating my monthly spending and net worth on a monthly basis on the same day that I pay my monthly bills. Because I have been diligent with this, the data has proven to be extremely useful in helping me to understand my finances in both spending and investment growth.
In my spreadsheet, I also have 2 graphs:
The first of which plots the last 4 years worth of spending, along with a 12 month moving average of this spending. This data has given me a very clear understand of how much money I will need on a monthly basis to maintain my current lifestyle And since my finances are quite simple, it is actually an easy exercise. In fact, I am not even very granular, as I have less than a dozen categories. I am not so much worried about where I spend it, but it is vital that I know exactly how much I spend. On this same graph, I also plot a line representing 4% of my total savings, (not including my paid off home, pensions, or Social Security) so that once this line rises above my 12 month moving average (mma) for monthly spend, it is very clear that I am completely FI. I have had several months where my individual monthly spend has been less than this 4% value, but I am still about $1000 apart from my 12 mma for monthly spend. Personally, I feel that this data is very important, and that everyone who chooses to act as their own financial planner is doing themselves a disservice if they are not plotting this - Knowledge is power!
The second plot is of my monthly new worth change, again, calculated at the same time as my monthly spending. I do not consider this graph to be nearly as important, however, I personally find it extremely interesting. I have seen my net worth change by as much as +$70k or -$90k in a 30 day period. But since I am very comfortable with the volatility of the market (including the 2007 crisis, and the dot.com bubble), I never panic or stray from regular investing. That said, I also calculate a 12 mma of the monthly change in my net worth. The key takeaway here is that line has continued to hover between +$10k and +$20k each month, even with wild swings in the market!
The important thing here is to continue to collect regular data today, as it will serve you well in the future.