Enter your last period date to instantly predict your next period, find your ovulation date, and know your fertile window — all in one free, private tool.
Predictions may shift ±3–5 days due to stress or hormonal changes.
A period tracker and calculator is a free digital tool that predicts your next period date, ovulation, and fertile window based on two simple inputs: the first day of your last menstrual period (LMP) and your average cycle length. Rather than guessing when your period will arrive — or being caught off guard — a period tracker puts you in control of your cycle every single month.
Our Bloom Health Woman Period Tracker uses a medically validated formula recommended by the American College of Obstetricians and Gynecologists (ACOG) to calculate your next period date, ovulation window, and the 6-day fertile window in which pregnancy is possible. It also estimates your next 3 cycles ahead — giving you a true period calendar, not just a one-time calculation.
A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the commonly cited average. Normal period duration is 3 to 7 days, with typical blood loss of 30–80 mL (roughly 2–6 tablespoons). However, what's "normal" for you is what matters most — and your baseline may differ from the textbook average.
| Cycle Feature | Normal Range | When to See a Doctor |
|---|---|---|
| Cycle length | 21–35 days | Consistently <21 or >35 days |
| Period duration | 3–7 days | Lasting more than 7 days |
| Blood loss | 30–80 mL per cycle | Soaking a pad/tampon per hour |
| Cycle variation | ±2–3 days month to month | Varying by more than 7–10 days |
| Missed periods | Occasional (stress, illness) | 3+ missed periods in a row |
A period calculator gives you a one-time prediction based on your last period and cycle length. A period tracker builds a running history across multiple cycles — making predictions smarter and more personalized as you log more data. Our tool does both: instant calculation right now, plus the ability to track your personal pattern over time for increasing accuracy.
For women with regular cycles, period trackers are highly accurate — typically within 1–3 days. Accuracy improves when you log actual period start dates each month rather than relying on a fixed cycle length estimate. Women with irregular cycles (common with PCOS, perimenopause, or high stress) may see predictions vary by 5 or more days — using a combination of our tracker plus OPK testing gives the most complete picture.
💡 Pro tip: Log your period start date every month — even if it's just a note in our tracker. After 3–6 cycles, your predictions become significantly more accurate and personalized to your unique pattern.
A period is considered late when it hasn't arrived within 5 days of its expected date. More than 7 days late is a missed period. At this point, if there's any chance of pregnancy, take a home pregnancy test. Missing 3 or more consecutive periods (called secondary amenorrhea) requires prompt medical evaluation regardless of pregnancy status.
Medical Disclaimer: This period tracker and all content on this page is for educational purposes only and does not constitute medical advice. Period predictions may vary ±3–5 days. Always consult a qualified healthcare provider for concerns about your menstrual cycle.
Our free period tracker and calculator uses the first day of your last menstrual period and your average cycle length to predict your next period date, ovulation date, and fertile window. The formula is based on the medically established principle that ovulation occurs approximately 14 days before your next period — meaning the calculation adjusts automatically for any cycle length, whether your cycle is 21 days or 35 days.
Unlike period tracking apps that require sign-up and data storage, our period tracker works entirely in your browser — no account, no personal data stored, and no advertisements based on your health information.
Once you calculate your results, our tracker shows your next period date plus estimates for the following two cycles — giving you a 3-month period calendar at a glance. This is particularly useful for planning around events, travel, or medical appointments, and for spotting any patterns in your cycle timing.
| Cycle Length | Ovulation Day | Fertile Window | Next Period |
|---|---|---|---|
| 21 days | Day 7 | Days 2–7 | Day 22 |
| 24 days | Day 10 | Days 5–10 | Day 25 |
| 26 days | Day 12 | Days 7–12 | Day 27 |
| 28 days (avg) | Day 14 | Days 9–14 | Day 29 |
| 30 days | Day 16 | Days 11–16 | Day 31 |
| 32 days | Day 18 | Days 13–18 | Day 33 |
| 35 days | Day 21 | Days 16–21 | Day 36 |
Period trackers are most accurate for women with regular, consistent cycles — typically predicting within 1–3 days. Accuracy improves when you log your actual period start dates each month. If your cycle varies by more than 7 days month to month, physical tracking (cervical mucus, OPK testing) gives more reliable real-time information than calendar calculation alone.
A period tracker uses two simple pieces of information — the first day of your last period and your average cycle length — to predict future dates. Your menstrual cycle begins on the first day of bleeding and ends the day before your next period starts. Most cycles range between 21 and 35 days, with 28 days being the average.
Once you enter your data, the tracker calculates your next expected period date, your ovulation window (typically 14 days before your next period), and your 6-day fertile window. These predictions become more accurate over time as you log multiple cycles and establish your personal pattern.
Tracking your menstrual cycle is one of the simplest and most powerful things you can do for your health. Here's why thousands of women in the USA make it a daily habit:
A period calculator gives you a one-time prediction based on your last period date and cycle length. A period tracker builds a history over multiple cycles — making predictions smarter and more personalized with every entry. Our tool does both: instant calculation today, with the ability to track patterns over time.
For women with regular cycles, period trackers are highly accurate — typically within 1 to 3 days. Accuracy improves when you log your actual period start dates rather than relying on a fixed cycle length. Irregular cycles (common with PCOS, perimenopause, or high stress) are harder to predict and may vary by 5 or more days. If your cycle is consistently unpredictable, use our Irregular Period Checker for personalized insights.