PERIODS
Estimate your next period, likely ovulation date and fertile window from the cycle information you enter.
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FREE MENSTRUAL CYCLE CALCULATOR — USE IT NOW
Enter basic information about your latest period to see an estimated next-period window, ovulation date and fertile window.
These dates show your estimated cycle timing based on the information entered. For pregnancy prevention, use a recognised contraceptive method.
*The information submitted in this calculator is not stored.
Cycles are personalA 28-day cycle is a common reference point. Cycle timing and period length can vary between women and from month to month.
Changes may be worth discussingSpeak with a gynaecologist if periods are repeatedly absent, suddenly change, are unusually heavy, cause severe pain, or regularly last outside your normal pattern.
A HELPING HAND FOR WHAT COMES NEXT
Talk through the estimate with Aura, or keep it with your dates so it is easy to find next time.
Create a free ParentAura+ App account to keep this dated result, follow changes and build a clearer report over time.
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WHAT YOUR ESTIMATE SHOWS
USEFUL TO KNOW
This is an estimation based on the details entered. Please consult your gynaecologist to confirm the outcome when it relates to your care.
UNDERSTANDING YOUR CYCLE
A menstrual cycle starts on the first day of one period and ends the day before the next period begins. Tracking the dates can help you anticipate bleeding, understand recurring symptoms and recognise changes in your usual pattern.
This is the date used to begin each cycle, even if bleeding continues for several days.
Many adult cycles fall between approximately 21 and 35 days, and small month-to-month changes can occur.
Period length counts bleeding days. Cycle length counts from the start of one period to the start of the next.
Several recorded cycles provide a more useful picture than a single calendar estimate.
The menstrual cycle is a repeating sequence of hormonal and physical changes that prepares the body for a possible pregnancy. It includes menstruation, development of an egg, ovulation and the time after ovulation.
This begins on the first day of the period. The uterine lining is shed, estrogen gradually rises and follicles in the ovaries develop. One follicle may release an egg at ovulation. The length of this phase can vary considerably.
This begins after ovulation. Progesterone helps prepare the uterine lining for a possible pregnancy. If pregnancy does not occur, estrogen and progesterone fall and the next period begins.
Mark the first day of one period, then mark the first day of the following period. Count the days from the first date up to—but not including—the second date. That number is the cycle length. Repeat this for several cycles and calculate an average if the lengths are reasonably consistent.
To make a simple next-period estimate, add the usual cycle length to the first day of the most recent period. The calculator also estimates ovulation by counting back approximately 14 days from the predicted next period. The time between ovulation and the next period is not exactly 14 days for every woman, so the result remains approximate.
Bleeding patterns differ. A period commonly lasts several days, often around two to seven days, but your usual pattern matters. Spotting is not always the same as the first day of full menstrual bleeding, so consistent recording helps.
Stress, illness, travel, major sleep changes, significant weight change, intense exercise, breastfeeding, adolescence, perimenopause, medicines and conditions such as PCOS or thyroid disorders can affect cycle timing. Tracking shows the pattern, while a medical professional can assess possible causes when needed.
If cycles are frequently shorter than about 21 days, longer than about 35 days, or vary widely, tracking can provide useful information to discuss with a gynaecologist.
A calculator predicts from an average, but an individual cycle may be longer. Pregnancy is one possibility after unprotected sex, while stress, illness, travel, major sleep or weight changes, intense exercise, breastfeeding, changes in contraception, PCOS, thyroid conditions and perimenopause can also alter timing.
A later-than-expected period can happen for different reasons. If pregnancy is possible, use an appropriately timed pregnancy test. Professional support can help when periods remain absent, repeatedly unpredictable or substantially different from your usual pattern.
Small differences between cycles are common. A pattern may be considered irregular when periods are repeatedly fewer than about 21 days or more than about 35 days apart, when the gap changes considerably from one cycle to the next, or when bleeding is unusually heavy or unpredictable.
A calculator becomes less accurate when cycles vary. Recording several start dates, bleeding days and symptoms is still useful because it turns “my periods are irregular” into a dated history that a gynaecologist can review.
Cramping can occur as the uterus contracts. Mild discomfort is common, but pain that interrupts normal activities, becomes suddenly worse or is not helped by usual measures deserves medical attention.
Hormonal changes may affect energy. Very heavy periods can also contribute to iron deficiency and fatigue, so persistent exhaustion alongside heavy bleeding should be discussed with a gynaecologist.
Hormonal changes can affect fluid balance and digestion. Speak with a clinician if bloating is severe, persistent or continues well beyond the usual cycle pattern.
Some women notice irritability, sadness, anxiety or emotional sensitivity before a period. Track timing and severity. Major mood symptoms or changes affecting daily life need professional support.
Hormonal fluctuations may be linked with temporary acne and breast tenderness. New or persistent breast symptoms deserve individual assessment from a qualified medical professional.
Yes, particularly with shorter cycles or longer bleeding. Sperm can remain alive for several days, and ovulation may happen earlier than a calendar estimate predicts. For pregnancy prevention, use a recognised contraceptive method.
One estimate assumes that the entered cycle length represents your usual pattern. Tracking several months can show average cycle length, variation, bleeding duration and recurring symptoms. This makes the dashboard more personal and provides clearer information if you later speak with a gynaecologist.
Cycle length naturally varies, but a recurring pattern of cycles shorter than about 21 days, longer than about 35 days, missed periods or large changes from one month to the next is worth discussing with a gynaecologist. Recording several cycles helps you see whether the change is occasional or repeating.
Stress, illness, travel, sleep changes, weight changes, breastfeeding, contraception, PCOS, thyroid conditions and pregnancy can all affect timing. If pregnancy is possible, take a pregnancy test at the appropriate time. Seek professional support for persistent or significant changes.
Yes. This can happen when ovulation occurs early, especially with shorter cycles or longer bleeding. Sperm can remain alive for several days, so period dates alone should not be used for contraception.
Enter the first day of your latest period and your usual cycle length to see an estimated next-period date, cycle phases and fertile-window timing.
Instead of relying on one month, the App compares the period dates and symptoms you record across multiple cycles. It shows your shortest, longest and average recorded cycle so your personal pattern becomes easier to understand.
A HELPING HAND FOR FUTURE DATES
The matching ParentAura+ App keeps the dates and updates you choose to add together, so your own pattern becomes easier to follow over time.
FREQUENTLY ASKED QUESTIONS
No. Every calculator gives its result without asking for an account or contact details.
No. Your entries stay in the browser while you calculate and are not automatically added to a ParentAura profile.
You can leave with the result, talk it through with Aura, or explicitly save it to a free ParentAura+ Account for ongoing tracking.
No. Calculators provide mathematical estimates and general planning information. A qualified medical professional provides diagnosis and treatment.