Period & cycle calculators
Every tool is free and calculates in your browser. Start from the question you have — each card says what you enter and what you get back.
Plan your cycle
Dates ahead, worked out from one period start.
Period Calculator
When is my next period?
- You enter
- first day of your last period, cycle length (or a few past start dates, or shortest and longest cycle), period length
- You get
- next period dates, ovulation estimate, fertile window, 6-month calendar
Cycle Phase
Which cycle day and phase am I in today?
- You enter
- first day of your last period, cycle length, period length
- You get
- today’s cycle day, estimated phase, ovulation and next-period dates
Period Calendar
What do the next 12 months look like?
- You enter
- first day of your last period, cycle length, period length, which layers to show
- You get
- a 12-month forecast calendar to print or share
Understand your pattern
Built from your own past dates — or, for a first period, body changes.
Period Tracker
Where do I keep my real start dates?
- You enter
- the first day of each period as it comes
- You get
- a log saved in this browser, your average cycle, next estimate
Printable Tracker
I’d rather track on paper.
- You enter
- nothing — download and print
- You get
- a 12-month dot calendar and a period journal (PDF, Letter or A4)
Cycle Length
How long are my cycles, really?
- You enter
- 2–6 past period start dates
- You get
- average cycle length, shortest and longest, a regularity check
Irregular Periods
My cycles vary — what range should I expect?
- You enter
- first day of your last period, shortest and longest recent cycle, period length
- You get
- date ranges for the next periods and fertile days
First Period Quiz
When might my first period come?
- You enter
- answers to 6 questions about body changes
- You get
- a rough time range — not a date
If your period is late
What the delay means and when a test or a doctor makes sense.
Late Period
My date has passed — how late am I?
- You enter
- first day of your last period, cycle length
- You get
- days past the expected date and what that usually means
Missed Period
Have I missed a whole period?
- You enter
- first day of your last period, cycle length
- You get
- how many expected dates have passed, test and see-a-doctor lines
Pregnancy Test
When will a test be reliable?
- You enter
- last period and cycle length — or expected period, date of sex, or ovulation date
- You get
- earliest, reliable and best days to test
Fertility & pregnancy
Calendar estimates around ovulation and pregnancy — not tests.
Ovulation
When am I most likely to ovulate?
- You enter
- first day of your last period, cycle length
- You get
- ovulation estimate, a realistic range, the 6-day fertile window
Conception
When did conception probably happen?
- You enter
- last period and cycle length — or your due date
- You get
- estimated conception date and the days of sex that could have led to it
Implantation
When could implantation happen?
- You enter
- first day of your last period, cycle length
- You get
- the 6–12-day window after estimated ovulation, and test timing
Due Date
When is my baby due?
- You enter
- last period (and cycle length), conception date, or IVF transfer date and embryo age
- You get
- due date, how many weeks pregnant, milestone dates
Not sure between two?
| You want to know | Use | What makes it different |
|---|---|---|
| My expected date has passed — how many days late is this? | Late Period | Counts days past one expected date |
| A whole period seems to be missing | Missed Period | Counts how many expected dates have gone by, with the 3-month line |
| Could I be pregnant — when is a test worth taking? | Pregnancy Test | Gives test days, from your period, a date of sex or ovulation |
| Which days could I get pregnant this cycle? | Ovulation | Looks ahead: ovulation estimate and the 6-day window |
| I’m pregnant — when did it probably happen? | Conception | Looks back from the last period or the due date |
| When could implantation happen this cycle? | Implantation | Shows the 6–12-day window after estimated ovulation — it can’t tell you what any spotting is |
| I want to see the coming months at a glance | Period Calendar | A forecast from one start date and your averages |
| I want to keep the dates my periods actually started | Period Tracker | Saves real dates in this browser and learns your average |
| Same, but on paper | Printable Tracker | PDF templates — nothing typed into a website |
This tool provides estimates for personal planning only and is not a substitute for professional medical advice, diagnosis or treatment. Predictions must not be used as contraception. If you have concerns about your cycle, heavy bleeding, severe pain or missed periods, please consult a licensed clinician.