The trick: put yourself in BCC. The email goes to your accountant on the 1st of every month, and a copy lands in your own inbox.
Why it works
You've made a public promise to a real person — and that's far harder to break than a private to-do item you can silently reschedule. The BCC copy sits in your inbox as the nagging proof that you committed. The email is identical every month; the pressure it creates is what's fresh.
Make it yours
Swap the accountant for anyone whose expectation you don't want to disappoint: a bookkeeper, a business partner, a mentor, a client. The pattern is the same — commit to a person, on a date, and copy yourself in.