Medication cycle calculator

Cycled schedules are the ones people lose track of: 21 days on and 7 off, an injection every 12 weeks, a week on and a week off. Enter the pattern once and this gives you the actual dates.

Why cycles slip

A daily medication rides on a daily habit. A cycled one does not: the trigger for the next start is a date you have to remember, and it moves every cycle. A 28-day cycle drifts through the week, so “I restart on Mondays” stops being true after the first month.

The fix is to stop computing it and write the dates down — which is all this page does. Print it, or put the next start in your calendar as soon as one finishes.

The break is part of the prescription

For plenty of cycled medications the days off are doing real work, not just resting the schedule. Shortening or skipping the break because it is inconvenient changes the treatment, and whether that is acceptable is a question for whoever prescribed it, not a judgement call to make from a calendar.

Equally, if a dose lands late, the right response depends on the medication — sometimes you take it and shift the cycle, sometimes you keep the original dates. Ask once, at the start, and write the answer down.

Long gaps need a supply plan

An every-12-weeks injection means four appointments a year, and appointments are booked weeks out. The gap that catches people is not the dose, it is the prescription renewal behind it — the refill date calculator covers the supply side, and Doz supports cycles such as 21 days on and 7 off directly, so the pattern lives in the app rather than on a printout.

Common questions

How do I work out the next start date of a 21-on-7-off cycle?

The cycle is 28 days long, so each one starts 28 days after the last. If the first day on was the 3rd, the next cycle starts on the 31st, then 28 days after that.

How many days is every 12 weeks?

84 days. Twelve weeks of seven days each, which is why an every-12-weeks injection drifts relative to the calendar month rather than falling on the same date.

What if I miss the start of a cycle?

It depends on the medication: for some you take it late and shift the whole cycle, for others you keep the original dates. That is a question for your prescriber or pharmacist, and worth asking at the start rather than in the moment.

One thing this cannot do

This is an arithmetic tool, not medical advice. It works out numbers from what you type in — it does not know your medication, your prescription, or what you should do if something goes wrong. Anything about changing a dose, spacing doses differently, or handling a missed dose is a question for your doctor or pharmacist.