Your six-month period calendar
Six months from 30 August 2026, built from a 28-day cycle that runs 25 to 31 days. Every predicted period is shaded as the window it might start in rather than as a single day, and the windows widen down the page because they have to.
A4 · one page
August 2026 to January 2027
28-day cycle · 25–31 day range
These are windows, not dates. Each estimated period is your cycle length added to 30 August 2026, again and again. The darker block is where that arithmetic lands; the pale run around it is every day the period could be happening, given that your own cycle runs 25 to 31 days. The last start window on this sheet is 37 days wide against the first one's 7, because every cycle in between can move and the movement adds up — across 612,613 cycles the mean movement in one person's own cycle length was 2.6 days from one cycle to the next. By the bottom of this page the pale run has swallowed most of the month, and that is the honest answer to what a calendar knows six cycles out.
Not contraception, and it cannot be made into contraception. Ovulation shifts, sperm can survive in the body for up to 7 days, and no calendar can see either. Followed imperfectly, fertility awareness is about 76% effective — 24 women in 100 get pregnant in a year — and the NHS does not officially recommend any app or device for it. There is no fertile shading on this sheet: that estimate is a back-count of 10 to 16 days from each predicted period, which is the NHS's own range and never a day 14, and it is on the calculator page with its sources and this refusal beside it.
General information, not medical advice. Write in what actually happened: one real date is worth more than all six of these. The NHS suggests speaking to a GP if your periods are irregular or your usual pattern changes.
To save a PDF instead of printing, choose Save as PDF as the destination in the print dialog, and set margins to None. Turn on background graphics if the shaded days come out blank. Free, and no account.
Everything on this sheet is arithmetic on the numbers in the address bar. It cannot see your body. A stressful month, an illness, travel or a change in sleep can move a cycle further than the window drawn here, and the sheet has no way to know that has happened.
It is not contraception, it cannot tell you whether you are pregnant, and it cannot diagnose anything. If your periods stop, if the gap between them keeps changing and that is new for you, or if something else about them worries you, that is a conversation with a clinician rather than a calendar.
Change the numbers on the period calculator and this sheet redraws. For a blank grid to fill in by hand instead, there is the printable period tracker, and for your own average and range there is the cycle length calculator.
Where this comes from
- NHS (2025). Periods. https://www.nhs.uk/conditions/periods/
- NHS (2025). Periods and fertility in the menstrual cycle. https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/
- NHS (2025). Irregular periods. https://www.nhs.uk/symptoms/irregular-periods/
- NHS (2024). Natural family planning (fertility awareness). https://www.nhs.uk/contraception/methods-of-contraception/natural-family-planning/
- npj Digital Medicine (PubMed Central) (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. https://pmc.ncbi.nlm.nih.gov/articles/PMC6710244/
- Human Reproduction Open (PubMed Central) (2020). Real-life insights on menstrual cycles and ovulation using big data. https://pmc.ncbi.nlm.nih.gov/articles/PMC7164578/
- American College of Obstetricians and Gynecologists (2023). Fertility Awareness-Based Methods of Family Planning. https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning
Every link above was checked when this page was last updated. Athena is not affiliated with any of these organisations, and none of them has reviewed this page. Nothing here is medical advice.