Based on Fabien Olicard's "Votre temps est infini"
Income / ((Work + Commute + Prep) × 4 weeks)
Think about tasks like cleaning, laundry, taxes, grocery delivery, etc.
Minimum someone should pay YOU to do this on your free time.
Note: If the delegation cost is lower than your RHV, it's mathematically profitable. If you hate the task, even if it's slightly more expensive than your RHV, consider your "Pain Threshold" (the subjective value of your peace of mind).