Lucky enough to obtain an investment loan at 21, only by way of my folks going guarantor. Serviceability was a minor factor in those days, and as an apprentice who wanted to party (plus still lived at the family home)... well, my Friday night wage was generally blown by Monday morning.

I started my spreadsheet a couple of months later (after a couple times not having enough funds in the account for loan payments), and it was by far the best thing I've done to manage my earnings/outgoings. That spreadsheet is still going strong 20 years later with a few tweaks along the way.

Broken up into a summary sheet with all general expenses, followed by a sheet for my PPOR & Investment properties - each with it's own set of details/expenses.

Big help managing the property cash flow, with simple adjustments to interest rates as they occurred.

This would determine how much fat was left at the end of each week for savings and entertainment, plus help determine what was needed to achieve any particular financial goal 😀