How do I calculate my next prescription refill date?

Add the day supply to your last fill date. For example, if you filled a 30-day prescription on June 1st, your next refill date is July 1st (June 1 + 30 days). Use our calculator above to instantly find your refill date for 28, 30, or 90-day prescriptions. Simply enter your last fill date and day supply, and the calculator shows your next refill date with the exact day of the week.

How do I calculate my next prescription refill date?

Add the day supply to your last fill date. For example, if you filled a 30-day prescription on June 1st, your next refill date is July 1st (June 1 + 30 days). Use our calculator above to instantly find your refill date for 28, 30, or 90-day prescriptions. Simply enter your last fill date and day supply, and the calculator shows your next refill date with the exact day of the week.

Prescription Refill Calculator

Last Fill Date

Day Supply

Refills Remaining

No refills

Insurance Early Refill

Apply insurance refill-too-soon rule

Calculate when you can next refill your prescription based on your last fill date and day supply.

Next Refill Date

Jul 4, 2026

On Schedule·30 days from now

Refill Details

Key dates and metrics for your prescription

Last Filled

Thursday, June 4, 2026

Runs Out

Jul 4, 2026

Days Until Refill

30days

Days Remaining

30days

Refills Remaining

0refills

Medical Disclaimer

Important safety and usage information

For informational purposes only. Not medical advice. Always follow your provider's and pharmacist's instructions.

Insurance rules vary by plan. The 75% and 85% thresholds are common guidelines. Your plan may differ. Controlled substances may have additional restrictions.

What is a Prescription Refill Calculator?

A simple tool to find your next medication refill date

Enter your last fill date and day supply — the calculator instantly shows your next refill date with the day of the week. It supports 28-day (controlled substances), 30-day (standard), and 90-day (maintenance) prescriptions.

Refill Formula

Next Refill = Fill Date + Day Supply

Example: June 1 + 30 days = July 1

How Prescription Refill Dates Are Calculated

Every refill formula you need — including reverse calculations

Calculate Next Refill Date

Next Refill = Fill Date + Day Supply

Calculate When Medication Runs Out

Runs Out = Fill Date + Day Supply

Calculate Total Days Covered

Total Days = Day Supply × (Refills Remaining + 1)

Calculate Day Supply From Pill Count

Day Supply = Total Pills ÷ Pills Per Day

Worked Examples

28-Day

Controlled substances

Filled Jun 1Jun 29

28-day supply

30-Day

Standard monthly

Filled Jun 1Jul 1

30-day supply

90-Day

Maintenance meds

Filled Jun 1Aug 30

90-day supply

Reverse Calculation Modes

When does it run out? Toggle to Runs Out mode — enter fill date + day supply to see days remaining and medication end date with a progress bar.
How many refills left? Toggle to Refills Left mode — enter refills remaining to see total coverage days, last possible fill date, and a full chronological refill schedule.
Pill-count mode: Switch to pill-count input — enter pills per day + total pills to automatically calculate your day supply.

Common Prescription Day Supply Periods

28-day, 30-day, and 90-day — when each is used and why

28-Day (Controlled)

Schedule II medications

Adderall, Ritalin, Oxycodone
Cannot be refilled — new Rx needed
2-day buffer for processing
13 fills per year (365 ÷ 28)

30-Day (Standard)

Most common prescription period

Blood pressure, cholesterol, antidepressants
Insurance allows refill at 75–85% used
~12 fills per year
Standard at most retail pharmacies

90-Day (Maintenance)

Long-term chronic medications

Thyroid, diabetes, chronic conditions
Often dispensed via mail-order
Only 4 pharmacy visits per year
Lower per-fill copay with many plans

Understanding Insurance Early Refill Rules

How the 75% and 85% rules determine your earliest refill date

75% Rule

Most common — used by major insurers

Refill allowed when three-quarters of your medication has been used. For a 30-day supply, you can typically refill around day 22–23.

28-day supply → refill after 21 days
30-day supply → refill after 22–23 days
90-day supply → refill after 67–68 days

85% Rule

Restrictive — some plans & controlled substances

More restrictive plans require 85% usage before allowing a refill. Common for certain controlled medications and high-cost specialty drugs.

28-day supply → refill after 23–24 days
30-day supply → refill after 25–26 days
90-day supply → refill after 76–77 days

Important: Insurance policies vary by plan and provider. Controlled substance prescriptions (Schedule II) often have stricter rules and may not allow early refills at all. Always verify with your pharmacy or insurance provider for your specific plan's policy.

How to Calculate Refills Remaining

Total coverage = day supply × (refills + 1)

Multiply your day supply by refills remaining plus one. The +1 accounts for your current fill.

Coverage Formula

Total Days = Day Supply × (Refills + 1)

Day Supply

30 days

Refills

Total Coverage

120 days

Tips for Never Missing a Prescription Refill

Practical strategies to stay on top of your medication schedule

Set Calendar Reminders

Find your refill date, then set a phone reminder 3–5 days before. Gives you time to contact your doctor if a new prescription is needed.

Enable Auto-Refill at Your Pharmacy

CVS, Walgreens, and Walmart offer free auto-refill. They fill your prescription automatically and notify you when it's ready.

Know Your Insurance Rules

Check whether your plan uses 75% or 85% early-refill. Use the insurance toggle above to avoid showing up too early.

Use Pill-Count Mode

Not sure about your day supply? Switch to pill-count mode. Enter pills per day and total pills to auto-calculate your refill date.

Plan for Weekends, Holidays & Travel

Check the refill schedule for dates that conflict. Contact your pharmacy 5–7 days ahead for early pick-up or vacation overrides.

Frequently Asked Questions

Common questions and detailed answers

A 28-day prescription can typically be refilled 28 days after the last fill date. However, insurance companies often allow an early refill when 75–85% of the medication has been used. For a 28-day supply at 75%, you may refill as early as day 21 (75% × 28 = 21 days). At 85%, the earliest would be day 23–24. Controlled substance prescriptions (Schedule II) like Adderall often require a new prescription each month rather than a refill. Use the calculator above with your specific fill date and insurance settings for your exact date.

28-day prescriptions are common for Schedule II controlled substances (like Adderall, Ritalin, Concerta, and certain pain medications). These medications typically cannot be refilled — a new, written prescription is required from your doctor each month. The 28-day cycle (rather than 30) provides a 2-day buffer for pharmacy processing, insurance authorization, and patient pickup. This buffer helps ensure continuity of care without gaps in medication. Some Schedule III–IV controlled substances may also use 28-day cycles depending on state laws and pharmacy policies.

Insurance companies use the "percent used" rule to determine when you can refill. Most plans allow a refill when 75% of your medication has been used — for a 30-day supply, that's around day 22–23. Some more restrictive plans require 85% usage (day 25–26 of a 30-day supply). Our calculator's insurance toggle lets you see the earliest refill date for both 75% and 85% thresholds. The formula is: Earliest Refill Date = Last Fill Date + (Day Supply × Early Refill %). For controlled substances, insurers may apply stricter rules or not allow early refills at all.

Check your prescription label or bottle — it will show "Refills Remaining: X" or "Refills: X before [date]." To calculate your total remaining coverage: multiply your day supply by (refills remaining + 1). The "+1" accounts for your current fill. For example, a 30-day supply with 3 refills remaining provides 30 × 4 = 120 total days of coverage. Our calculator does this automatically when you enter your refills remaining count. You can also use the refill schedule to see each future refill date.

28-day prescriptions are typically used for controlled substances (Schedule II–IV) and provide a 2-day buffer each month for processing and pickup. 30-day prescriptions are the standard for most non-controlled medications like blood pressure drugs, cholesterol medications, and antidepressants. The key difference: 28-day prescriptions result in 13 fills per year (365 ÷ 28 = 13.04), while 30-day prescriptions result in about 12 fills per year. This affects your pharmacy visit frequency and annual out-of-pocket costs. Some insurance plans may also cover 28-day and 30-day supplies at different copay tiers.

Most insurance plans allow refills on 90-day prescriptions when 75% of the medication has been used — around day 67–68. Some plans may require 85% usage (day 76–77). Unlike 28 or 30-day prescriptions, 90-day supplies are typically for maintenance medications (thyroid, cholesterol, blood pressure) and are often dispensed through mail-order pharmacies. Because the supply is larger, pharmacies and insurers may apply different early-refill rules. Always check with your pharmacy or insurance provider for your specific plan's 90-day early refill policy.

Day supply is the number of days your medication is intended to last when taken as prescribed. Your next refill date is calculated simply as: Last Fill Date + Day Supply. For example, a 30-day supply filled on June 1 means you can refill on July 1. A 90-day supply filled on June 1 means you can refill on August 30. Insurance companies may allow you to refill slightly earlier (see the 75% and 85% rules above). Our calculator supports all common day supply periods (28, 30, 90 days) plus custom day supplies from 1 to 365 days.

Missing your refill date generally means you can refill anytime after that date — you are not limited to a narrow time window. There is no "late penalty" for most medications. However, for controlled substances, your doctor may have written specific "do not fill until [date]" or "must last until [date]" instructions. If you miss a refill date by more than a few days, you may also run out of medication, which can be dangerous for conditions like high blood pressure, diabetes, or heart disease. Use our calculator to plan ahead and set calendar reminders 3–5 days before each refill date.

Pharmacies calculate refill dates by adding the prescribed day supply to the date the medication was last dispensed (filled). For example: Date Filled (June 1) + Day Supply (30 days) = Refill Date (July 1). Pharmacies then check against insurance company rules, which typically allow refills when 75–85% of the medication has been used. For controlled substances, pharmacies follow stricter federal and state regulations — they may use exact day-count from the fill date without any early-refill window. Some pharmacies also use "refill too soon" alerts in their computer systems that automatically flag attempts to refill before the insurance-allowed date.

Embed Prescription Refill Calculator

Add this calculator to your website or blog for free.

Related calculators from other categories

Last updated Jun 4, 2026