The one-line practical rule:
If you need to remember an action, it's a reminder. If you need to track money moving, it's an expense (even when the amount is still TBD).
Decision table
| Situation | What is it? | Why |
|---|---|---|
| Electricity bill, you pay it every cycle | Expense | It's a certain monetary movement |
| Car tax renewal, due in 2 months | Expense | You'll pay — the amount is predictable |
| Call the accountant about tax forms | Reminder | The action is "call", not "pay" |
| Yearly boiler check-up | Reminder | Amount depends on what they find; the action is "do the check" |
| Call the doctor about a booster vaccine | Reminder | There's not always a cost |
| Home insurance, due on Sep 30 | Expense | You'll pay — even if the bill arrives in July |
Three clarifying examples
1. Bill vs Boiler check-up
The electricity bill is an expense: arrives every two months, you pay, done. Even when you don't know the exact amount a month ahead, you use "Expense with TBD amount" — see TBD amounts for the pattern.
The yearly boiler check-up is a reminder: the action is "call the technician and do the check-up" by October 15. If the technician later sends you an invoice, you record it as a new expense then (or convert it from the reminder — see below).
2. Mortgage instalment vs Tax forms
The mortgage instalment is an expense you pay every month, even when it runs on autopay and you don't have to lift a finger. It's a certain monetary movement: you want it in the expense calendar, in the budget-health dashboards, in the reports.
The tax forms with the accountant is a reminder: the action is "call the accountant" by end of month. If a payment request eventually shows up, they'll be the one telling you the amount and the date. At that point the reminder can turn into an expense.
3. Insurance vs Doctor appointment
The home insurance is an expense, even when you'll pay it in July and it's still February. You know it's coming; you want it in the calendar and in "Upcoming 30 days" as it approaches.
The call to the doctor about Luca's vaccine is a reminder. Maybe the vaccine will be free (public health system), maybe there's a co-pay — you don't know and it's not the point. The action is to call and not forget about it.
When in doubt: start from the verb
If the person describing the task would use an action verb ("call", "check", "remember to"), it's a reminder.
If they'd use a monetary noun ("pay the bill", "wire the tax", "settle the invoice"), it's an expense — even when the amount is still TBD.
And if mid-stream a reminder becomes an expense? One click registers it as expense while preserving the audit trail.