Prescription Refill Calculator
Free medication refill date calculator with advanced tracking for tablets, liquids, and controlled substances.
Advanced Prescription Refill Calculator
Calculate refill dates, days supply, and manage multiple medications with pharmacy-specific policies
Common: 28, 30, or 90 days
- Set phone reminders 3-5 days before refill date
- Enable automatic refills at your pharmacy
- Keep this calculator bookmarked for easy access
Total quantity dispensed
e.g., 0.5, 1, 1.5, 2
Bottle size in milliliters
Amount per dose
Total doses in inhaler
Puffs each time
Number of pens/syringes
Usually 1
e.g., 1.5 for once + half dose
Medication Tracker
Manage multiple prescriptions and sync refill dates
Medication Schedule Summary
How do you calculate day supply for liquids?
Calculating days supply for liquid medications requires a simple formula that pharmacies use daily. The calculation determines how long a liquid prescription will last based on the total volume dispensed and the patient's dosing instructions.
Days Supply = Total Volume (mL) ÷ (Dose Volume per Administration × Frequency per Day)
Example 1: A patient receives a 120mL bottle of liquid antibiotic. The directions state "Take 5mL twice daily." The calculation is: 120mL ÷ (5mL × 2 times per day) = 120 ÷ 10 = 12 days supply.
Example 2: A cough syrup prescription is for 240mL with instructions to "Take 10mL three times daily." Days supply = 240mL ÷ (10mL × 3) = 240 ÷ 30 = 8 days supply.
Rx refill calculator vs OTC refill calculator
Prescription (Rx) refill calculators and over-the-counter (OTC) medication calculators serve different purposes and follow distinct rules for medication management.
Prescription Refill Calculator: This tool is designed for medications that require a doctor's prescription. It accounts for pharmacy-specific refill policies, insurance company restrictions, controlled substance regulations (Schedule II-V), and early refill allowances. Rx calculators must factor in the 28-day rule for 30-day supplies and calculate when insurance will approve the next refill.
OTC Refill Calculator: Over-the-counter medications don't require prescriptions and have no refill restrictions. An OTC calculator simply helps track when you need to purchase more medication based on your usage pattern. There are no insurance limitations, pharmacy policies, or controlled substance rules to consider.
- Rx calculators enforce pharmacy and insurance refill policies
- Rx calculators account for controlled substance restrictions
- OTC calculators focus only on personal inventory management
- Rx calculators calculate earliest allowable refill dates (usually 2-3 days early)
Our prescription refill calculator is specifically designed for Rx medications and includes features for CVS, Walgreens, Walmart, and other major pharmacy chains. It automatically applies the correct early refill policy based on medication type and pharmacy selected.
How do you calculate day supply for tablets?
Calculating days supply for tablets and capsules is the most common pharmacy calculation. This determines how many days a prescription will last and when the patient can request a refill.
Days Supply = Total Quantity Dispensed ÷ (Tablets per Dose × Frequency per Day)
Example 1 - Simple Dosing: A patient receives 30 tablets with directions "Take 1 tablet once daily." Days supply = 30 ÷ (1 × 1) = 30 days supply.
Example 2 - Multiple Tablets per Dose: Prescription for 60 tablets with directions "Take 2 tablets twice daily." Days supply = 60 ÷ (2 × 2) = 60 ÷ 4 = 15 days supply.
Example 3 - Partial Tablets: Prescription for 45 tablets with directions "Take 1.5 tablets once daily." Days supply = 45 ÷ (1.5 × 1) = 30 days supply.
Example 4 - Variable Dosing: Some medications have tapering doses. For a prednisone taper: 21 tablets taken as "3 tablets daily for 3 days, 2 tablets daily for 3 days, 1 tablet daily for 3 days" = 9 days total supply.
The 28-day prescription refill rule means most 30-day supplies can be refilled after 28 days (approximately 2 days early). This allows flexibility for patients while preventing excessive early refills. Always verify the day supply calculation matches the pharmacy label to avoid refill issues.
How to use the medication refill calculator
Our prescription refill calculator provides three powerful tools to manage your medications effectively. Follow these step-by-step instructions to get accurate refill dates and days supply calculations.
Refill Date Calculator
- Enter Fill Date: Select the date you picked up your prescription from the pharmacy. This is printed on your medication label.
- Enter Days Supply: Enter the days supply (typically 28, 30, or 90 days). This is also on your pharmacy label.
- Select Pharmacy: Choose your pharmacy (CVS, Walgreens, Walmart, etc.) to apply their specific early refill policy.
- Choose Medication Type: Select whether this is a regular medication or controlled substance. Controlled substances have stricter refill rules.
- Calculate Early Refill (Optional): Check this box to see the earliest date your pharmacy and insurance will allow a refill.
- Click Calculate: View your next refill date, days until refill, and pharmacy-specific policies.
Days Supply Calculator
- Select Medication Form: Choose tablets, liquids, inhalers, or injections.
- Enter Total Quantity: Input the total amount dispensed (number of tablets, mL of liquid, puffs in inhaler, etc.).
- Enter Dose Amount: Specify how much you take each time (1 tablet, 5mL, 2 puffs, etc.).
- Select Frequency: Choose how often you take the medication per day (once, twice, three times, etc.).
- Calculate: The calculator shows your total days supply with the complete formula breakdown.
Multi-Medication Tracker
- Click "Add Medication": Create entries for each of your prescriptions.
- Fill in Details: Enter medication name, fill date, and days supply for each prescription.
- View Schedule: See all refill dates sorted chronologically with color-coded alerts for upcoming refills.
- Track Multiple Meds: The tracker automatically saves your medications locally for easy access.
This 30-day prescription calculator and 90-day prescription calculator works for all common prescription types. The rx refill calculator follows the same policies used by pharmacies nationwide, ensuring your calculations match what the pharmacy will tell you.
FAQs
How do you calculate prescription refill date?
To calculate a 30-day prescription refill date: (1) Take your fill date, (2) Add 29 days to find your last dose date, (3) Add one more day for the refill date. For example, if you filled a prescription on January 1, your last dose is January 30, and your refill date is January 31. For 28-day prescriptions add 27 days, and for 90-day prescriptions add 89 days.
What is the 28 day prescription refill rule?
The 28-day refill rule means insurance companies and pharmacies require at least 28 days to pass before approving a refill on a 30-day prescription. This represents approximately 80% medication usage. The rule prevents early refills and medication stockpiling, especially for controlled substances.
How early can I refill my prescription at CVS or Walgreens?
CVS Pharmacy: Regular medications can be refilled 3–5 days early. Controlled substances are limited to 2 days early. Walgreens: Standard medications allow 3-day early refills, controlled substances allow 2 days early. Walmart: Allows up to 4 days early for regular medications. Always confirm with your pharmacy location.
How do you calculate days supply for liquid medications?
Days supply for liquids is calculated as: Total volume (mL) ÷ (Dose volume × Daily frequency). Example: 120mL bottle with 5mL doses taken twice daily = 120 ÷ (5 × 2) = 12 days supply.
Can controlled substances be refilled early?
Controlled substances have strict refill limits. Most pharmacies allow refills only after 75–80% usage (typically 2 days early for 30-day supplies). Schedule II medications usually require a new prescription and cannot be refilled early.
What is the difference between 28-day and 30-day prescriptions?
A 28-day prescription provides exactly four weeks of medication, while a 30-day prescription provides a full month. Insurance plans often allow refills after 28 days even for 30-day prescriptions, enabling a 2-day early refill window.
How does the 90-day prescription calculator work?
For 90-day prescriptions, add 89 days to the fill date to find the last dose date, then add one more day for the refill date. Most pharmacies allow refills 7–10 days early on 90-day supplies.
Why was my prescription refill denied?
Common reasons include refilling too early, no refills remaining, prescription expiration, insurance authorization issues, or controlled substance monitoring restrictions. Contact your pharmacy or healthcare provider for clarification.
Trusted Medical Resource
For official medication information, dosing guidelines, and safety details, visit MedlinePlus – U.S. National Library of Medicine . This government-maintained resource provides accurate, evidence-based medication guidance.