You are calculating "Days Supply". Rx: 30 tablets. Sig: 1 tab BID. How many days will it last?
Answer choices
- A30 days
- B60 days
- C10 days
- D15 days
About this question
How do you calculate days supply when the sig is 1 tablet BID and the quantity is 30 tablets? Days supply divides total quantity by daily dose. Order Entry items check whether you build the daily dose from the frequency abbreviation before you divide.
BID means twice daily, so the patient takes 2 tablets per day. Thirty tablets divided by 2 equals 15 days. Insurance billing, refill timing, and counseling all depend on that order of operations — frequency → daily dose → days supply.
Reveal answer & explanationShow
Correct answer
- A30 days
- B60 days
- C10 days
- D15 daysCorrect
Basic rationale
Daily dose = 1 tab x 2 times = 2 tabs/day. Total 30 tabs / 2 tabs per day = 15 days supply.
Option explanations
- A: Incorrect. This assumes 1 tab/day (QD); BID requires 2 tabs/day.
- B: Incorrect. This multiplies 30 × 2; days supply requires division.
- C: Incorrect. 10 days would apply to TID (30 ÷ 3), not BID.
- D: Correct. 30 tablets ÷ 2 tabs/day (BID) = 15 days supply.
Deep Analysis
Core logic
Days supply = total quantity ÷ daily usage. BID = twice daily, so daily use = 1 tab × 2 = 2 tabs/day. Days supply = 30 tablets ÷ 2 tabs/day = 15 days.
Distractor analysis
A: 30 days assumes only 1 tab/day (QD), ignoring the BID frequency. B: 60 days incorrectly multiplies quantity × frequency instead of dividing. C: 10 days uses TID (3×/day) math: 30 ÷ 3 = 10, but the Sig says BID.
Exam trap
The #1 days-supply mistake: multiplying instead of dividing. Formula is always quantity ÷ daily dose, never quantity × frequency.
Memory tip
📅 Divide, don't multiply: Days Supply = Total Quantity ÷ Daily Dose. BID here = 2/day → 30 ÷ 2 = 15.
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