The year starts with $20K budget. Each time a nickel is spent, it is deducted. Fertilizer, feed, meds, fuel, hydraulics, lease, tires - everything. Equipment depreciation does not figure in to the budget but it does figure in to income taxes. Most years there are a few nickels left of the budget.
I calve year round so I sell pretty much year round. Used to sell some hay too. That all goes into a different tally. It had best be above $20K at the end of the year. Sometimes it is significantly bigger. Maybe I go and buy a new cutter with the extra. Usually buy and lot of T posts, rolls of wire etc regardless. If profit is marginal, I don't buy anything.
It works for me. Kind of personal information but I truly don't mind sharing it.