I've gotten this question a number of times, and I understand it. Gas feels mandatory, like rent, because we need it to commute to work. So should we add it to our list of fixed expenses?

The definition I use in Tend for a fixed expense is a committed payment for a known amount on a known date to a known merchant.

If you sat at home and did nothing for an entire month, you'd still be charged for a fixed expense. Rent, insurance, subscriptions, and memberships are examples.

A discretionary expense is something you actively purchase. You are present when you swipe your card. You get to choose the merchant you buy from and the amount you spend.

Therefore, by my definitions, gas is discretionary. You may spend roughly the same amount each month, but you actively choose when, where, and how much to buy.

This is my bold bet with Tend:

If it's not a fixed expense, don't set aside money for it.

Instead, focus on your total discretionary allowance for the week. Let that single number, along with your intuition, guide how you spend that lump sum. If we spend here, we know to cut back there, just for this week. People seem to do this naturally without any budget software at all.

This approach has two benefits:

1. Less time managing your budget - you're tracking just one number instead of juggling separate budgets for gas, groceries, entertainment, clothes, and dining out.

2. Your spending habits will actually change - A single true limit on what you can spend in total for a week forces you to make real tradeoffs in the moment when it matters.

It may be a little uncomfortable at first, but I urge you to give this system a try. It's working for me and I've been trying to find a good budgeting system for 18 years. It might work for you too.