How to calculate days' supply (tablets and liquids)
Days' supply tells insurers how long a fill should last. It is quantity ÷ amount used per day, rounded down to whole days.
Method
- Work out the amount used per day: (amount per dose) × (doses per day).
- Divide the quantity dispensed by the daily amount.
- Round down to a whole number of days.
Worked examples
Example 1
Sig: take 2 tablets by mouth three times daily (TID). Quantity dispensed: 30 tablets. What is the days' supply? (Days' supply is reported in whole days, rounded down.)
Show solution
- Tablets per day = 2 × 3 = 6
- Days' supply = 30 ÷ 6 = 5
- Round down to 5 days
Answer: 5 days
Example 2
Sig: 15 mL by mouth 2 times daily. A 100 mL bottle is dispensed. What is the days' supply? (Round down to whole days.)
Show solution
- mL per day = 15 mL × 2 = 30 mL
- Days' supply = 100 ÷ 30 = about 3.33
- Round down to 3 days
Answer: 3 days
Example 3
Sig: take 2 tablets by mouth twice daily (BID). Quantity dispensed: 180 tablets. What is the days' supply? (Days' supply is reported in whole days, rounded down.)
Show solution
- Tablets per day = 2 × 2 = 4
- Days' supply = 180 ÷ 4 = 45
- Round down to 45 days
Answer: 45 days
Tips
- BID = 2, TID = 3, QID = 4 doses a day.
- For liquids, convert everything to mL first (1 tsp = 5 mL, 1 tbsp = 15 mL).
- Insurers may apply their own rules for inhalers, insulin and eye drops. Follow the plan's guidance.
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