Plan when to refill prescriptions.
Days of supply is the units in hand divided by the units consumed per day, where daily consumption is doses per day multiplied by units per dose — the step people most often skip when a prescription is two tablets twice daily. Subtracting the pharmacy's turnaround from that figure gives the day to place the order rather than the day you run out, which is the number that actually prevents a gap in therapy.
Days of supply
Days of supply = units on hand / (doses per day x units per dose)
Order date
Order in days = days of supply - pharmacy turnaround days
Educational estimate only. Not medical advice — discuss results with a qualified clinician before changing treatment, medication or exercise.
Use your realistic average for a PRN medication. Entering the maximum permitted frequency will make the calculation conservative, which is the safer error for a rescue inhaler or analgesic.
Prior authorisations, back-orders and public holidays routinely add days. A three-day buffer covers ordinary delay; chronic medications where interruption matters deserve more.