Medication Days Supply Calculator
Use this medication days supply calculator to estimate how long a prescription quantity may last. Enter the quantity dispensed and the amount used per day to calculate estimated days covered.
This is a planning and education tool only, not dosing or medical advice.
Enter prescription details
Example: 0.5, 1, or 2.
Example: 1, 2, 3, or 4.
Enter a date to estimate run-out date.
Estimated days supply
1 units/day
30 days
How do you calculate medication days supply?
Days supply is estimated by dividing the quantity dispensed by the amount used each day. This is a basic math estimate based on the numbers entered and is used for planning purposes.
For tablets or capsules, calculate daily use by multiplying units per dose by doses per day. For liquids, calculate daily mL use by multiplying mL per dose by doses per day.
The result is a math estimate and may differ from pharmacy or insurance calculations. Differences can happen because of how label directions are interpreted, partial fills, or system rules.
Days supply formula
For tablets or capsules:
Daily use = units per dose x doses per day
Days supply = quantity dispensed / daily use
For liquids:
Daily mL use = mL per dose x doses per day
Days supply = total mL dispensed / daily mL use
- 30 tablets / 1 tablet per day = 30 days
- 60 tablets / 2 tablets per day = 30 days
- 90 tablets / 1 tablet per day = 90 days
- 300 mL / 10 mL per day = 30 days
Medication days supply examples
| Quantity dispensed | Daily use entered | Estimated days supply | Example type |
|---|---|---|---|
| 30 tablets | 1 per day | 30 days | once-daily tablet |
| 60 tablets | 2 per day | 30 days | twice-daily tablet |
| 45 tablets | 1.5 per day | 30 days | fractional tablet example |
| 90 capsules | 1 per day | 90 days | 90-day supply example |
| 300 mL liquid | 10 mL per day | 30 days | liquid medicine example |
These examples are for math planning only. Follow the instructions on your prescription label and ask your pharmacist or prescriber about medication-use questions.
Days supply examples
Example 1: 30 tablets, 1 tablet per day — 30 / 1 = 30 days.
Example 2: 60 tablets, 1 tablet twice daily — 1 tablet x 2 doses per day = 2 tablets per day. 60 / 2 = 30 days.
Example 3: 300 mL liquid, 5 mL twice daily — 5 mL x 2 doses per day = 10 mL per day. 300 / 10 = 30 days.
Why pharmacy days supply may be different
Specialized days supply calculators
What this days supply calculator cannot tell you
Days supply calculator FAQ
How do I calculate days supply?+
Divide the quantity dispensed by the amount used per day. For example, 30 tablets at 1 tablet per day equals about 30 days by basic math. The result is an estimate based on the numbers entered.
What is days supply for a prescription?+
Days supply is an estimate of how many days a prescribed quantity may last based on the daily amount entered. It is used for planning and pharmacy math. It is not a guarantee of how long the medication will last.
How do I calculate days supply for tablets?+
Calculate daily use by multiplying units per dose by doses per day. Then divide the quantity dispensed by the daily use. For example, 1 tablet twice daily equals 2 tablets per day. 60 tablets divided by 2 equals 30 days.
How do I calculate days supply for capsules?+
The same math applies as for tablets. Calculate daily use by multiplying capsules per dose by doses per day. Then divide the quantity dispensed by the daily use. For example, 90 capsules at 1 capsule per day equals about 90 days.
How do I calculate days supply for liquid medicine?+
Calculate daily mL use by multiplying mL per dose by doses per day. Then divide the total mL dispensed by the daily mL use. For example, 300 mL at 5 mL twice daily equals 10 mL per day. 300 divided by 10 equals 30 days.
What if I take half a tablet per day?+
Enter 0.5 in the units used per dose field or use the direct units per day field. The calculator supports fractional amounts. For example, 30 tablets at 0.5 tablets per day estimates about 60 days.
What if the directions say as needed?+
Directions like "as needed" or "PRN" may not translate into a single daily amount. The calculator requires a daily use value entered by you. Your pharmacy or insurance system may calculate days supply differently for as-needed medications.
Why is my pharmacy days supply different from my estimate?+
Differences may happen because of label interpretation, as-needed directions, partial fills, package sizes, insurance system rules, or pharmacy policy. This calculator provides a math estimate only and may not match pharmacy or insurance calculations.
Can this calculator tell me when I can refill?+
No. This calculator estimates days supply, not refill dates. For refill-date math, use the Prescription Refill Date Calculator. Actual refill timing depends on your pharmacy, insurance plan, prescriber, medication, and local rules.
Should I ask my pharmacist if the days supply looks wrong?+
Yes. If the estimated days supply differs significantly from what you expect, ask your pharmacist or prescriber before making any changes. You can also review the Medical Disclaimer.
About this days supply calculator
This calculator uses basic quantity math to estimate medication days supply from the numbers entered. It is designed for planning and education only. It is not medical, dosing, legal, insurance, or dispensing advice.
Related resource: Days Supply Cheat Sheet — A printable reference sheet with days-supply formulas, examples, and practice problems.