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Calculation Machine

Days Supply Calculator

Pharmacy days-supply for tablets, liquids, inhalers and insulin.

Reviewed by James Whitfield · How we check our maths

Your values

Tablets, mL, or units.

ⓘ Live results

Results
Days supply
30 days
Amount used per day
2
Quantity for 30 days
60
Quantity for 90 days
180

Working

  1. 1Per-day use = 1 × 2 = 2
  2. 2Days supply = 60 ÷ 2 = 30

Quick answer

Days supply = total quantity dispensed ÷ total amount used per day. For a 30-tablet bottle taken twice daily, days supply = 30 ÷ 2 = 15 days.

The formula

Days supply = quantity dispensed ÷ (dose × doses per day)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Quantity dispensed60
  • Amount per dose1
  • Doses per day2

Result

  • Days supply30 days
  • Amount used per day2
  • Quantity for 30 days60
  • Quantity for 90 days180

How to use the Days Supply Calculator

  1. 1Enter the quantity dispensed.
  2. 2Enter the dose size and how many times a day it is taken.
  3. 3Read the days supply and the 30/90-day quantities.
Quantity dispensed
Tablets, mL, or units.

Frequently asked questions

How do you calculate days supply for insulin?

Add up the total units used per day across all injections, then divide the total units dispensed (for example 1000 units in a box of five 3 mL pens at 100 units/mL) by that daily total.

Do you round days supply up or down?

Insurers almost always require rounding down to whole days, so a 15.6-day calculation is billed as 15 days.

About this calculator