It’s simple!

1. Basic Mode: Enter the date you last filled your prescription (“Fill Date”) and the number on your bottle for “Days Supply” (e.g., 30 or 90).
2. Advanced Modes: If you don’t know the days supply, select the “Tablets” or “Liquid” tab. Enter your fill date and the details from your prescription label (total quantity, dose, frequency).

The calculator will instantly show your next refill date, days remaining, and earliest possible refill date.

The next refill date is calculated by adding the “Days Supply” to the “Last Fill Date.” For example, if you filled a 30-day supply on November 1st, the next refill date would be 30 days later, on December 1st.

“Days supply” is the total number of days your prescribed medication will last if you take it exactly as directed. This is a crucial number used by pharmacists and insurance companies to determine your refill schedule. Your prescription label will almost always state the days supply (e.g., “30-day supply” or “90-day supply”).

You can calculate this by dividing the total number of tablets in the bottle by the number of tablets you take each day.

Formula: Days Supply = Total Tablets / (Tablets per Dose × Doses per Day)

Example: Your bottle has 60 tablets, and your instructions are “Take 1 tablet 2 times per day.”
60 / (1 * 2) = 30 days.

This requires a few steps:

1. Find your dose in mL: Dose (mg) / Concentration (mg/mL) = Dose (mL)
2. Find total mL used per day: Dose (mL) * Doses per Day = Total mL/day
3. Find days supply: Total Volume in Bottle (mL) / Total mL/day = Days Supply

Our “Liquid” tab does this math for you automatically.

Insulin pens are similar to liquid calculations. A standard insulin pen (like Lantus or Humalog) contains 3mL of insulin, and the concentration is almost always 100 units/mL. This means one pen contains 300 units.

Formula: Days Supply = (Total Units in Pen) / (Units per Dose × Doses per Day)

Example: You take 20 units, 1 time per day.
300 units / (20 units * 1) = 15 days per pen.

If your prescription is for a box of 5 pens, your total days supply is 15 days/pen * 5 pens = 75 days.

This is an estimate, as drop size varies. Pharmacists use a standard estimate of 15 to 20 drops per 1 mL. Let’s use 15 drops/mL for a conservative estimate.

Example: You have a 5mL bottle, and the directions are “1 drop in each eye, 2 times per day.”

1. Total Drops: 5 mL * 15 drops/mL = 75 drops total
2. Drops per Day: 1 drop * 2 eyes * 2 times/day = 4 drops per day
3. Days Supply: 75 drops / 4 drops/day = 18.75 days.

A pharmacist would likely dispense this as an 18-day supply.

The 80% rule is a common insurance policy stating that you must have used at least 80% of your medication before they will cover the cost of a refill. For a 30-day supply, this means you can get a refill after day 24 (30 * 0.80 = 24). This allows for a 6-day buffer in case you are traveling or there is a pharmacy delay.

Yes, the same rule usually applies. If your insurance uses the 80% rule, you can refill a 90-day supply after 72 days (90 * 0.80 = 72). This gives you an 18-day window to get your refill before you run out.

Insurance companies and pharmacies allow early refills (e.g., at the 80% or 90% mark) for several practical reasons:

• Travel: It allows you to get your medication before going on vacation.
• Convenience: It gives you a buffer of several days, so you don’t have to go to the pharmacy on the exact day you run out.
• Closures: It accounts for pharmacy closures on weekends or holidays.
• Delays: It provides time for the pharmacy to order your medication if it’s not in stock.

Yes. A “30-day supply” refers to 30 consecutive calendar days, which includes weekends and holidays. The calculation is a simple addition of days to the fill date.

Rules for controlled substances (e.g., opioids, stimulants) are much stricter. Many states and insurance plans do not follow the 80% rule for these medications. A common rule for Schedule II-V drugs is that they cannot be refilled more than 2 days early, regardless of the supply length. Always check with your pharmacist, as state and federal laws are the final authority.

If you miss a dose, your medication will last longer than the original “days supply.” For example, if you miss 2 doses during a 30-day supply, you will have 2 extra doses at the end. This means your “real” supply lasts 32 days. However, your *insurance* will still only authorize a refill based on the original 30-day schedule. Missed doses generally do not affect your refill eligibility date.

This typically refers to the rule for controlled substances. It means you can pick up your refill a maximum of 2 calendar days before your “Next Refill Date.” For a 30-day supply filled on November 1st (due Dec 1st), you could refill it as early as November 29th.

Tapered doses (where your dose changes over time) require a manual calculation. You must calculate the number of days for each dosage level and add them together.

Example: “Take 2 tablets per day for 7 days, then 1 tablet per day for 7 days.”

• Phase 1: 2 tablets/day * 7 days = 14 tablets
• Phase 2: 1 tablet/day * 7 days = 7 tablets
• Total: 14 + 7 = 21 tablets for a 14-day supply.

Prescription Date: The date the doctor *wrote* the prescription.
Fill Date: The date the pharmacy *dispensed* the medication to you.

Your refill schedule is always based on the Fill Date, not the date the doctor wrote it.

This calculator cannot tell you how many refills you have left. To find this, look at your prescription label. It will usually say “Refills Remaining: 2” or similar. You can also call your pharmacy, and they can look it up for you.

Yes! After you calculate a schedule, a “Download .ics File” button will appear. Clicking this will download a standard iCalendar file that you can import into Google Calendar, Apple Calendar, Outlook, and most other calendar applications.

Yes. This calculator is 100% private. All calculations are done directly in your web browser (client-side). No information you enter is ever sent to our server or stored anywhere. You can disconnect from the internet, and it will still work.

“As needed” or “PRN” prescriptions do not have a standard days supply. The pharmacist and insurance company will make a “best guess” based on the maximum allowed dose.

For example, if a pain medication says “Take 1 tablet every 4-6 hours as needed,” the pharmacist will calculate the supply based on the *maximum* dose (1 tablet every 4 hours, or 6 tablets per day) to ensure you are covered. If you use it less, it will simply last longer.

This message means you have not yet reached the “earliest possible refill date” allowed by your insurance. This is based on the 80% or 90% rule. If you are traveling and need an exception, you can call your insurance company and ask for a “vacation override.”