Period Calculator
Predict your next period dates for the next 6 months
Period Details
For informational purposes only.
Enter your period details and click Calculate
Days Until Next Period
— days
Next 6 Periods
| # | Start Date | End Date | Days Away |
|---|
How to Use
- Enter the First Day of Your Last Period.
- Enter your Average Cycle Length (default 28 days).
- Enter your Average Period Duration (default 5 days).
- Click Calculate to see your next 6 periods with start and end dates.
- The result also shows how many days until your next period begins.
How the Period Calculator Works
A menstrual cycle is counted from the first day of one period to the first day of the next. The calculator adds your average cycle length repeatedly to predict future period dates. The end of each period = start date + period duration − 1.
What is a Normal Menstrual Cycle?
| Parameter | Normal Range | Average |
|---|---|---|
| Cycle length | 21–35 days | 28 days |
| Period duration | 2–7 days | 5 days |
| Blood loss | 30–80 ml | ~40 ml |
When to See a Doctor
- Cycles shorter than 21 days or longer than 35 days consistently
- Periods lasting more than 7 days or very heavy flow (soaking more than 1 pad/hour)
- Skipping 3 or more periods (if not pregnant)
- Severe pain that disrupts daily activities
- Spotting between periods
Factors That Affect Cycle Regularity
- Stress and significant lifestyle changes
- Significant weight gain or loss
- PCOS (Polycystic Ovary Syndrome) — the most common hormonal disorder
- Thyroid conditions (hypo/hyperthyroidism)
- Starting, stopping, or changing hormonal contraception
Frequently Asked Questions
For women with regular cycles, predictions are quite accurate within ±1–3 days. For women with irregular cycles (varying by more than 7 days), accuracy decreases significantly. The calculator assumes your future cycles will match the cycle length you enter. Stress, illness, travel, and hormonal changes can all shift period timing.
PMS (Premenstrual Syndrome) occurs in the luteal phase — typically 7–14 days before your period. Symptoms include mood changes, bloating, breast tenderness, fatigue, and food cravings. For most women this is 7–10 days before the next period. Severe PMS is called PMDD (Premenstrual Dysphoric Disorder) — if symptoms significantly impair daily life, consult a gynaecologist.
Yes — certain hormonal contraceptives allow you to skip or delay periods. Extended-cycle oral contraceptive pills (taken continuously for 3 months) reduce periods to 4 per year. Some IUDs (hormonal) significantly reduce or eliminate periods. NuvaRing and contraceptive patches can also be used in extended cycles. Discuss options with your doctor.
A missed period (not due to pregnancy) is called amenorrhea. Primary amenorrhea: never having had a period by age 15–16. Secondary amenorrhea: missing 3+ consecutive periods in someone who previously had regular cycles. Common causes: pregnancy (always test first), stress, extreme exercise, significant weight loss, PCOS, thyroid disorders, or early menopause. See a doctor if you miss 3+ periods.