Days Supply Calculator
Calculate medication days supply based on quantity and dosing schedule.
How to Use
- Enter the total quantity of medication dispensed (number of pills, tablets, capsules, etc.)
- Enter the number of doses per day as prescribed
- Enter the number of units (pills/tablets) taken per dose
- Click Calculate to see how many days the supply will last
- Review the total number of doses in the supply
What is Days Supply?
Days supply is the number of days a medication will last based on the quantity dispensed and the prescribed dosing instructions. It's a critical metric used in pharmacy practice, insurance billing, and medication management to ensure patients have appropriate access to their medications.
Accurate days supply calculations are essential for proper medication adherence, preventing early refills, and ensuring insurance coverage requirements are met. Pharmacists calculate days supply for every prescription filled to determine when a patient will need their next refill.
How to Calculate Days Supply
The days supply calculation is straightforward: divide the total quantity of medication by the number of units taken per day.
Formula: Days Supply = Total Quantity / (Doses Per Day × Units Per Dose)
- Total Quantity: The number of units dispensed (tablets, capsules, mL, etc.)
- Doses Per Day: How many times per day the medication is taken
- Units Per Dose: How many units are taken each time (e.g., 2 tablets per dose)
Common Medication Scenarios
| Scenario | Quantity | Dosing | Days Supply |
|---|---|---|---|
| Standard prescription | 30 tablets | 1 tablet daily | 30 days |
| Twice daily medication | 60 tablets | 1 tablet twice daily | 30 days |
| Multiple tablets per dose | 90 tablets | 3 tablets once daily | 30 days |
| As-needed medication | 30 tablets | Up to 2 tablets daily | 15 days minimum |
Why Days Supply Matters
- Insurance Coverage: Most insurance plans have specific rules about when refills can be processed based on days supply
- Medication Adherence: Helps patients plan when to request refills and avoid running out
- Controlled Substances: Accurate calculations are legally required for controlled medications
- Cost Management: Prevents early refills that may not be covered by insurance
- Safety: Ensures appropriate quantities are dispensed to minimize risk of overdose or misuse
- Inventory Management: Helps pharmacies maintain appropriate stock levels
Special Considerations
Certain medications require special attention when calculating days supply:
- Tapering doses: Days supply may vary as the dose changes over time
- PRN (as-needed) medications: Calculate based on maximum daily dose
- Split tablets: Account for tablets that are cut in half
- Liquid medications: Calculate based on mL per dose
- Inhalers: Based on number of actuations, not just the device
- Combination packs: May have different quantities of different medications
Planning Your Refills
Understanding your medication's days supply helps you plan refills effectively:
- Request refills 7-10 days before running out to avoid gaps in therapy
- Check your insurance's refill-too-soon policies (usually 75-80% of days supply)
- Keep track of prescription expiration dates (typically valid for 1 year)
- Consider mail-order pharmacy for 90-day supplies if available
- Set calendar reminders based on your days supply calculation
- Coordinate with your pharmacy's automatic refill programs
Frequently Asked Questions
- What if I take different doses throughout the day?
- If you take different amounts at different times (e.g., 2 tablets in the morning and 1 at night), add up all the tablets you take in one day and use that as your total daily quantity. For example, 2 + 1 = 3 tablets per day. Then divide your total quantity by 3 to get days supply.
- When can I get my prescription refilled?
- Most insurance plans allow refills when you've used about 75-80% of your medication. For a 30-day supply, this is typically around day 22-24. However, policies vary by insurance company and medication type. Check with your pharmacy or insurance provider for specific refill rules.
- How do I calculate days supply for liquid medications?
- For liquid medications, use the same formula but with milliliters (mL) instead of tablets. For example, if you have 150 mL and take 5 mL twice daily, the calculation is: 150 ÷ (2 × 5) = 15 days supply. Always use the measuring device provided with your medication for accurate dosing.
- What about PRN or as-needed medications?
- For as-needed (PRN) medications, pharmacies typically calculate days supply based on the maximum daily dose. For example, if you're prescribed 'Take 1-2 tablets every 6 hours as needed,' the maximum is 8 tablets per day. A 30-tablet supply would be calculated as a minimum 3.75-day supply (30 ÷ 8 = 3.75 days).