Prescription Quantity Calculator

Calculate how many tablets or units to prescribe, or how many days a supply will last.

By Dr Amer Sheikh, GP Updated 17 October 2026 Clinical review pending

Runs in your browser. Nothing you enter is stored or sent anywhere.

How it works

Quantity = dose units × doses per day × days

Enter a quantity instead to see how many days it covers.

Tips

Round to whole packs where your formulary prefers it.
Check maximum quantities for controlled drugs (30 days).
Synchronise repeats where possible.

Frequently asked questions

How do I work out tablets for a course?

Multiply units per dose by doses per day by the number of days.

What is the maximum supply for controlled drugs?

Normally no more than 30 days for Schedule 2, 3 and 4 drugs.

Does this work for liquids?

Yes, if you enter the dose in mL.

Every tool you use, on one free desk

Prescription quantity is one of more than 150 UK primary care tools on MedToolbox. Pin your favourites and sync them to every device. Free for healthcare professionals, always.

Open MedToolbox

Related tools

References

Department of Health. Safer management of controlled drugs: 30-day prescribing guidance.

MedToolbox supports, and does not replace, clinical judgement, national guidance and local policy.