{
    "name": "Medication Days Supply Calculator",
    "url": "https://calculators.geekmidst.com/calculators/medication-days-supply-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/medication-days-supply-calculator.md",
    "category": "Healthcare operations",
    "description": "Work out a prescription’s days supply from the quantity dispensed and the prescribed directions (units per dose and doses per day), with any units left over.",
    "summary": "Days supply is the quantity dispensed divided by the units used per day under the prescriber’s directions. It does not choose or check a dose.",
    "also_called": [
        "Day supply calculator",
        "Prescription duration calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "quantity",
            "label": "Quantity dispensed",
            "type": "number",
            "default": "50",
            "unit": "units"
        },
        {
            "name": "per_dose",
            "label": "Units per dose",
            "type": "number",
            "default": "2",
            "unit": "units"
        },
        {
            "name": "doses_per_day",
            "label": "Doses per day",
            "type": "number",
            "default": "2"
        }
    ],
    "outputs": [
        {
            "key": "days_supply",
            "label": "Days supply",
            "format": "number"
        },
        {
            "key": "whole_days",
            "label": "Full days covered",
            "format": "integer"
        },
        {
            "key": "units_per_day",
            "label": "Units used per day",
            "format": "number"
        },
        {
            "key": "left_over",
            "label": "Units left after the full days",
            "format": "number"
        }
    ],
    "formula": {
        "text": "Days supply = Quantity dispensed ÷ (Units per dose × Doses per day)",
        "variables": {
            "Quantity dispensed": "total units supplied",
            "Units per dose": "tablets, mL, drops or puffs taken each time",
            "Doses per day": "how many times a day, from the directions"
        }
    },
    "worked_example": {
        "inputs": {
            "quantity": "50",
            "per_dose": "2",
            "doses_per_day": "2"
        },
        "steps": [
            "A 2.5 mL bottle at 20 drops/mL holds 50 drops; one drop in each eye is 2 drops per dose.",
            "Daily use = 2 drops × 2 times = 4 drops.",
            "Days supply = 50 ÷ 4 = 12.5 days (12 full days, 2 drops left)."
        ],
        "result": "A 50-drop bottle used one drop in each eye twice a day lasts 12.5 days, the figure in CMS’s pharmacy billing job aid."
    },
    "interpretation": "Use the result for billing and refill planning. Products dosed on a cycle (weekly patches, rings with a break week) need the cycle length, not a simple count: CMS bills four weekly patches as 28 days.",
    "assumptions": [
        "The patient follows the directions exactly, every day.",
        "The quantity and the dose use the same unit."
    ],
    "limitations": [
        "“As needed” directions, tapering doses and cyclical products need manual calculation.",
        "Drops per mL vary between products; use the manufacturer’s figure."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "How do I work out days supply for an inhaler?",
            "answer": "Divide the actuations in the inhaler by the puffs used per day. A 120-dose inhaler at 4 puffs a day is a 30-day supply."
        },
        {
            "question": "Should I round days supply up or down?",
            "answer": "Follow your payer’s rules. Many systems take the whole number of days the supply fully covers."
        }
    ],
    "sources": [
        {
            "title": "CMS: Pharmacy Auditing and Dispensing Job Aid — Billing Other Dosage Forms",
            "url": "https://www.cms.gov/medicare-medicaid-coordination/fraud-prevention/medicaid-integrity-education/downloads/pharmacy-selfaudit-jobaid-billing-other.pdf"
        }
    ],
    "related": [
        {
            "name": "Prescription Refill Date Calculator",
            "url": "https://calculators.geekmidst.com/calculators/prescription-refill-date-calculator"
        },
        {
            "name": "Pharmacy Stock Expiry Calculator",
            "url": "https://calculators.geekmidst.com/calculators/pharmacy-stock-expiry-calculator"
        },
        {
            "name": "Medical Inventory Reorder Calculator",
            "url": "https://calculators.geekmidst.com/calculators/medical-inventory-reorder-calculator"
        }
    ],
    "disclaimer": "This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.",
    "publisher": "GM¹X CalcVerse"
}