Day Supply Calculations (Tablets, Capsules, Lozenges)
Table of Contents
Day supply calculations determine how long a prescribed medication will last based on the quantity dispensed and the dosing schedule. These are crucial for insurance billing, patient adherence, and pharmacy workflow.
Day Supply Calculation Formula
Standard Daily Dosing (QD, BID, TID, QID)
Consider Total Quantity Written/Dispensed: 60 Tablets / Capsules
QD (Once Daily Dose)
- Prescription: Take one tablet once daily
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (1)
BID (Twice Daily Dose)
- Prescription: Take one tablet twice daily
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (2)
TID (Three Times Daily Dose)
- Prescription: Take one tablet three times daily
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (3)
QID (Four Times Daily Dose)
- Prescription: Take one tablet four times daily
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (4)
Half Tablet Dosing (QD, BID, TID)
Consider Total Quantity Written/Dispensed: 60 Tablets (Capsules should not be broken, crushed, or split in half)QD (Once Daily Dose)
- Prescription: Take half tablet (½) once daily
- ½ Tablet = 0.5
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (½)
BID (Twice Daily Dose)
- Prescription: Take half tablet (½) twice daily
- ½ Tablet = 0.5
- ½ Tablet twice daily = (½+½) 1 Tablet per day
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (1)
TID (Three Times Daily Dose)
- Prescription: Take half tablet (½) three times daily
- ½ Tablet = 0.5
- ½ Tablet three times daily = (½+½+½) 1.5 Tablet per day
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (1.5)
QID (Four Times Daily Dose)
- Prescription: Take half tablet (½) four times daily
- ½ Tablet = 0.5
- ½ Tablet four times daily = (½+½+½+½) 2 Tablets per day
- Quantity Written/Dispensed: 60
- Formula: Total Qty dispensed (60) / Tablets per day (2)
Different Dosing Frequencies (QD, BID, TID, QID)
| Dosing Schedule | Qty Dispensed | Tablets/Day | Day Supply |
| ½ Tab – QD | 60 | 0.5 | 120 |
| ½ Tab – BID | 60 | 1 | 60 |
| ½ Tab – TID | 60 | 1.5 | 45 |
| ½ Tab – QID | 60 | 2 | 30 |
| 1 Tab – QD | 60 | 1 | 60 |
| 1 Tab – BID | 60 | 2 | 30 |
| 1 Tab – TID | 60 | 3 | 20 |
| 1 Tab – QID | 60 | 4 | 15 |
| 2 Tab – QD | 60 | 2 | 30 |
| 2 Tab – BID | 60 | 4 | 15 |
| 2 Tab – TID | 60 | 6 | 10 |
| 2 Tab – QID | 60 | 8 | 7.5 (8 days) |
Tapering Dose
What is Tapering Dose?
A tapering dose means gradually reducing the dosage of a medication over time instead of stopping it abruptly. This is done by decreasing the dose in a stepwise fashion to allow the body to adjust.Why Is Tapering Important in Pharmacy?
Prevents Withdrawal Symptoms
Sudden discontinuation of certain medications (like corticosteroids, antidepressants, opioids, or benzodiazepines) can cause withdrawal symptoms or rebound effects. Tapering allows the body to slowly adapt.Reduces Risk of Adverse Effects
Tapering minimizes potential side effects like dizziness, nausea, or agitation.Allows Monitoring and Adjustment
Pharmacists and providers can observe the patient’s response at lower doses and adjust therapy if needed.Protects Hormonal Balance
For example, corticosteroids like prednisone suppress adrenal function—tapering gives the adrenal glands time to resume normal cortisol production.- Prescription: Prednisone 20 mg tablets
- Sig:
- Take 60 mg daily for 3 days, then
- 40 mg daily for 3 days, then
- 20 mg daily for 3 days.
Solution: Break down the tapering schedule:
- 60 mg daily for 3 days → 3 days
- 40 mg daily for 3 days → 3 days
- 20 mg daily for 3 days → 3 days
Answer: 9 days supply
- Prescription: Prednisone taper using 10 mg tablets
- Sig:
- Take 40 mg daily for 5 days, then
- 20 mg daily for 5 days, then
- 10 mg daily for 5 days.
Solution: Break down the tapering schedule:
- 40 mg daily for 5 days → 5 days
- 20 mg daily for 5 days → 5 days
- 10 mg daily for 5 days → 5 days
Answer: 15 days supply
Alternate Dosing
Alternate dosing refers to a medication regimen where the dose or frequency varies on different days, rather than remaining the same every day. This method is often used in tapering, titrating, or minimizing side effects while maintaining therapeutic benefit.
Types of Alternate Dosing Patterns:
- Alternating Strengths Daily – e.g., 50 mg one day, 25 mg the next.
- Alternating Number of Tablets – e.g., 1 tablet Mon-Wed-Fri, 2 tablets on other days.
- Every Other Day Dosing – common in corticosteroid tapering.
Question 1: Alternating Daily Doses
A patient is prescribed atenolol with the following instructions:- Take 50 mg on odd days and 25 mg on even days.
- You dispense 20 tablets of 50 mg and 20 tablets of 25 mg.
Explanation:
- The patient alternates doses every day: one day 50 mg, next day 25 mg.
- So, in 2 days, the patient uses:
- 1 tablet of 50 mg (odd day)
- 1 tablet of 25 mg (even day)
- Total number of 2 day sets = 20 tablets of each strength (20 sets).
- 20 sets × 2 days = 40 days supply
Question 2: Alternating 1 Tablet and 2 Tablets
A patient is prescribed Warfarin with instructions:- Take 1 tablet on Monday, Wednesday, and Friday. Take 2 tablets on other days.
- You dispense 17 tablets total.
Explanation:
- Days with 1 tablet: Mon, Wed, Fri = 3 days/week
- Days with 2 tablets: Tue, Thu, Sat, Sun = 4 days/week
- In 1 full week, the patient uses: (3 × 1) + (4 × 2) = 3 + 8 = 11 tablets/week
- To find how many days 17 tablets last: Let’s divide 17 by 11 tablets/week ≈ 1.545 weeks Then multiply: 1.545 weeks × 7 days/week ≈ 10.8 days
- Round down to 11 days supply
PRN Dosing (As Needed)
PRN Meaning: Patients may not take the medication every day, may take it as and when needed.
Solution: Use maximum possible day supply based on allowed doses.
Solution: Use maximum possible day supply based on allowed doses.
Question:
Explanation:
- Prescription: Take 1 tablet every 6 to 8 hours as needed (use maximum possible 4 tablets (Q6h) per day, instead of 3 tablets (q8h) per day).
- Quantity Dispensed: 60 tablets
Explanation:
- Maximum doses per day: The prescription allows for 1 tablet every 6 hours, which is a maximum of 4 tablets per day (since 24 ÷ 6 = 4).
- Day supply: Total quantity dispensed/Max. doses per day = 60/4 = 15 days
