Enter the first day of your last period and your recent cycle range to see your cycle day, expected window, and how many days late you are.
If pregnancy is possible, use the result to time a pregnancy test. If you have severe or one-sided pelvic pain, shoulder pain, weakness, dizziness, fainting, or heavy bleeding, get urgent medical help now rather than waiting for the calendar.
If you are not pregnant, a late period means ovulation came later than usual this cycle, or has not happened yet, because your period arrives around two weeks after you ovulate.
What does the calculator result mean?
Your cycle starts on the first day of menstrual bleeding. If that was 36 days ago, you are on cycle day 37. The calculator compares today's date with the window in which your next period would start if this cycle resembled your recent ones.
For example, if your recent cycles lasted 27 to 32 days:
- if fewer than 27 days have passed since day one, you have not reached your usual start-date window;
- when 27 to 32 days have passed, today is inside that window;
- once more than 32 days have passed, the result shows how many days you are beyond it.
The calculator uses your own range rather than day 28, because a normal cycle differs from one woman to the next. The International Federation of Gynecology and Obstetrics uses 24 to 38 days as the population-level range for usual cycle frequency in adults (Munro, Critchley and Fraser 2018). A 35-day cycle may be ordinary for one person and a real change for someone whose period almost always starts by day 27.
If your cycles vary a lot, enter the shortest and longest you have had recently. Your window will be wide, because your ovulation is arriving at a different point each cycle.
Is my period late by 1, 5, 7, 10, or 14 days?
Count those days from the end of your usual window, as the calculator does.
One day beyond your usual window is a small calendar change. If pregnancy is possible, testing can begin from the first expected day. A correctly used negative at five or seven days beyond your usual range is more informative than one taken on day one.
There is no universal maximum number of days a non-pregnant period can be delayed. A cycle can lengthen substantially or a period can be absent. That does not mean you should wait indefinitely. Arrange a routine assessment when a clear change keeps happening, when cycles are repeatedly far outside your usual range, or when you have had no period for three months without an already-understood reason. Seek advice earlier if you are trying to conceive, have new symptoms, or pregnancy remains possible.
When should I take a pregnancy test?
Most home pregnancy tests can be used from the first day of a missed period, but a negative result at that point is not conclusive. The US Food and Drug Administration says 10 to 20 out of every 100 pregnant people may not detect the pregnancy on the first day of a missed period, because many women have irregular periods and may miscalculate when their period is due (FDA pregnancy-test guidance).
If you know when your period was due, follow the test instructions and test from that date. If the result is negative and your period still has not started, repeat the test after several days. First-morning urine may improve the chance of detection when testing early. If a second test is negative and your period has still not arrived, contact a clinician rather than treating two negatives as an absolute rule-out.
If you do not know when your period was due, the NHS advises testing at least 21 days after the most recent unprotected sex (NHS pregnancy-test guidance). A test cannot detect a pregnancy caused by sex that happened too recently.
If unprotected sex was within the past five days and pregnancy is not wanted, contact a clinician or pharmacist promptly about emergency contraception. Do not wait for a late period to make that decision (CDC contraceptive guidance).
Can a late-period calculator tell me whether I ovulated?
No. It counts days, but your body can show you whether you did.
Basal body temperature may show a temperature rise after ovulation has probably occurred. Cervical mucus and urine luteinizing hormone tests can help identify a fertile window. Calendar apps are estimates, especially when cycles are variable (ACOG fertility-awareness guidance).
Women with PCOS rarely ovulate at the predicted time, because our hormones make our cycles a little wonky, so pay closer attention to your cervical mucus: it shows you when your body is gearing up to release an egg.
Why might a period be late?
Pregnancy is the first possibility to check when it applies. After that, look at what has changed recently, because anything that delays ovulation delays your period.
Possible contributors include:
- an ordinary one-cycle variation;
- a recent illness, major stressor, substantial change in food intake or weight, or intense exercise;
- starting, stopping, missing, or changing hormonal contraception or another medication;
- the months after pregnancy, including breastfeeding;
- perimenopause;
- thyroid or prolactin disorders;
- an ovulatory disorder such as PCOS/PMOS;
- primary ovarian insufficiency or another less common medical cause.
More than one can apply. A clinician may use your pregnancy risk, cycle record, age, symptoms, medications, examination, and selected tests to narrow the possibilities. The American Society for Reproductive Medicine describes pregnancy testing as the first step in secondary amenorrhea evaluation, followed as appropriate by tests such as thyroid-stimulating hormone, prolactin, follicle-stimulating hormone, and estradiol (ASRM amenorrhea guidance).
Does a late period mean PCOS or PMOS?
Very long cycles and missing periods are a common feature of PCOS, now called PMOS in the current international consensus (Teede and colleagues 2026), but one late period on its own is not enough to diagnose it. In adults, assessment generally requires two of three features after other causes are excluded: irregular cycles or ovulatory dysfunction, clinical or biochemical androgen excess, and polycystic ovarian morphology. Adolescents require a different approach, and ultrasound or anti-Müllerian hormone should not be used to diagnose them.
In adults more than three years after menarche and before perimenopause, the current guideline counts cycles longer than 35 days, shorter than 21 days, fewer than eight cycles a year, or any one cycle longer than 90 days as irregular (Teede and colleagues 2023).
If your periods are often late, especially with jawline acne, facial hair growth or scalp hair loss, ask your doctor for a proper PCOS/PMOS assessment: those three are signs of excess androgens, the defining feature of PCOS.
If your signs point to PCOS but it hasn't been confirmed, see your doctor first, because late periods can also come from undereating or intense exercise, and that needs more food rather than less. If you have PCOS, the first step is working out which of the four root causes, Insulin-Resistant, Adrenal, Post-Pill or Inflammatory, is affecting your ovulation and cycle length. My free root cause quiz tells you which it is, and The PCOS Repair Protocol gives you the step-by-step plan to reverse it so you can start ovulating naturally again.
What changes the answer?
Hormonal contraception
Some methods make bleeding lighter, irregular, or absent, so the date of a withdrawal bleed may not behave like an untreated menstrual cycle. Pregnancy is less likely when a reliable method has been used correctly and consistently, but contraception does not make pregnancy impossible. Check the instructions for missed or late doses and ask a clinician or pharmacist when the method or pregnancy risk is unclear (CDC contraceptive guidance 2024).
After pregnancy and while breastfeeding
Periods can remain absent while breastfeeding, but ovulation can happen before the first visible period. The CDC's lactational amenorrhea criteria require all three conditions for low pregnancy risk: no periods, fully or nearly fully breastfeeding, and less than six months since birth (CDC contraceptive guidance). If any condition does not apply, do not use the absence of a period as contraception.
Perimenopause
Cycles often become less predictable during the menopausal transition, but pregnancy remains possible until menopause is established. Bleeding after menopause, defined retrospectively after 12 months without a period, needs assessment rather than a calculator result (ACOG perimenopausal bleeding guidance).
Bleeding that stopped and returned
If bleeding started, stopped, and then came back, that is a bleeding-pattern question rather than simply a late-period calculation. Use the guide to a period that stops and starts again to separate a brief pause near the end from bleeding that returns days later, occurs after sex, or needs urgent care.
When should I seek urgent or routine care?
Get urgent medical help if pregnancy is possible and you have abnormal bleeding with pelvic or abdominal pain. Seek emergency care for sudden or severe pain, one-sided pelvic pain, shoulder pain, weakness, dizziness, fainting, or collapse. These can be warning signs of ectopic pregnancy, including before you know you are pregnant (ACOG ectopic pregnancy guidance).
Seek emergency care if you are changing a pad or tampon every hour for more than two hours and also have chest pain, shortness of breath, lightheadedness, or dizziness (ACOG abnormal uterine bleeding guidance).
Arrange routine care if:
- your period has been absent for three months without an already-understood reason;
- the change repeats or your cycles remain markedly different from your previous pattern;
- you have symptoms such as nipple discharge when not breastfeeding, new headaches or vision changes, hot flushes at an unexpectedly young age, or signs of androgen excess;
- you are trying to conceive and cycles are irregular or absent;
- pregnancy tests remain negative but your period does not return.
Bring the dates of bleeding and spotting, test dates and results, contraception and medications, recent health or weight changes, and any pain or other symptoms.
The calculator gives you a date boundary. Use it to make the next decision: test at the right time, watch one small variation, or take a persistent or symptomatic change to someone who can investigate it.
