Period Calculator
Calculate your menstrual cycle and predict next period dates
Enter the start date of your last menstrual period
Typical range: 21-35 days (28 is average)
How long your period typically lasts
Affects prediction accuracy
Your Cycle Prediction
Current Cycle Phase
This Month
Common Cycle Examples
| Cycle Length | Period Length | Next Period | Ovulation Day |
|---|---|---|---|
| 28 days | 5 days | Day 29 | Day 14 |
| 30 days | 6 days | Day 31 | Day 16 |
| 26 days | 4 days | Day 27 | Day 12 |
| 32 days | 7 days | Day 33 | Day 18 |
Period Cycle Report
Generated by SabiCalculator Period Calculator
How It Works: Calculate Your Menstrual Cycle
This period calculator helps you track your menstrual cycle, predict your next period, and identify your fertile window. Whether you’re planning for pregnancy, tracking your health, or just want to be prepared, understanding your cycle is essential.
Formula:
Next Period = Last Period + Cycle Length
Ovulation = Next Period – 14 days
Where Cycle Length is your average menstrual cycle duration
Understanding Your Menstrual Cycle Phases
The menstrual cycle has four main phases: menstrual, follicular, ovulation, and luteal. Each phase serves a different purpose in your reproductive health.
| Phase | Duration | Key Events | Hormones |
|---|---|---|---|
| Menstrual | 3-7 days | Period bleeding | Low estrogen |
| Follicular | 7-10 days | Egg development | Rising estrogen |
| Ovulation | 24 hours | Egg release | LH surge |
| Luteal | 10-14 days | Uterine lining thickens | Progesterone rise |
What is a Normal Menstrual Cycle?
A normal menstrual cycle typically lasts between 21 and 35 days, with bleeding lasting 2 to 7 days. The average cycle is 28 days, but many healthy women have cycles that vary from this average.
For Students:
Your cycle might be irregular during high school and college years. Stress, changing sleep patterns, and lifestyle changes can affect cycle regularity. This is normal for many young women.
For Working Adults:
Work stress, travel, and lifestyle factors can impact your cycle. Tracking helps you anticipate changes and manage symptoms more effectively.
Calculating Ovulation and Fertile Window
Ovulation typically occurs about 14 days before your next period starts. Your fertile window includes the 5 days before ovulation and the day of ovulation itself.
Example: If you have a 30-day cycle, ovulation occurs around day 16 (30 – 14 = 16). Your fertile window would be days 11-16 of your cycle.
Important:
Sperm can live in the female reproductive tract for up to 5 days. This means pregnancy can occur from intercourse that happens several days before ovulation.
Common Cycle Tracking Mistakes
Many people make errors when tracking their menstrual cycles. Here are the most common mistakes:
Mistake 1: Counting from the wrong day
Day 1 of your cycle is the first day of menstrual bleeding, not spotting.
Mistake 2: Assuming a 28-day cycle
Only about 13% of women have exactly 28-day cycles. Your normal might be different.
Mistake 3: Not tracking symptoms
Tracking symptoms like cramps, mood changes, and cervical mucus helps identify patterns.
When to See a Doctor About Your Cycle
While some variation is normal, certain signs may indicate a health concern. Consult a healthcare provider if you experience:
- Cycles shorter than 21 days or longer than 35 days consistently
- Bleeding that lasts more than 7 days
- Severe pain that interferes with daily activities
- No period for 90 days (without pregnancy)
- Sudden changes in your regular cycle pattern
- Excessive bleeding (soaking through a pad/tampon every hour)
Frequently Asked Questions
How accurate is this period calculator?
This calculator provides estimates based on your average cycle length. Accuracy depends on how regular your cycles are. For irregular cycles, predictions are less reliable.
Can stress affect my period?
Yes, stress can delay ovulation and cause irregular cycles. High stress levels can lengthen your cycle or cause skipped periods.
How do I know if I’m ovulating?
Signs of ovulation include: mild pelvic pain (mittelschmerz), changes in cervical mucus (becomes clear and stretchy), slight rise in basal body temperature, and increased libido.
Is it normal for cycles to vary?
Yes, it’s normal for cycles to vary by a few days each month. Variation of up to 7-9 days between your shortest and longest cycles is common.
Can I get pregnant during my period?
While unlikely, it’s possible, especially if you have short cycles. Sperm can survive for several days, and early ovulation can occur.
How long should I track before I see patterns?
Track for at least 3-6 months to identify your personal patterns. The more data you collect, the more accurate predictions become.
Tips for Accurate Cycle Tracking
For best results with this period calculator and your cycle tracking:
- Track consistently: Mark the first day of your period every month
- Note symptoms: Record cramps, mood changes, and other symptoms
- Consider lifestyle factors: Note stress, travel, illness, or medication changes
- Use a dedicated app or calendar: Physical or digital tracking works
- Give it time: Patterns emerge over several months, not weeks
- Update your averages: Adjust your cycle length input as you gather more data
Cycle Health and Wellness
Your menstrual cycle is a vital sign of your overall health. Regular cycles typically indicate good hormonal balance and reproductive health.
For Students:
Irregular cycles are common during teenage years and college. As your body matures, cycles often become more regular. If concerns persist past age 20, consult a healthcare provider.
Nutrition and Exercise:
Extreme dieting or excessive exercise can cause irregular periods or amenorrhea (missing periods). Balanced nutrition supports regular cycles.
Privacy Note:
This period calculator runs entirely in your browser. No data is sent to any servers. Your cycle information stays private on your device.
This period calculator is designed to help you understand and predict your menstrual cycle. While it provides helpful estimates, it should not replace medical advice. For concerns about your menstrual health, always consult with a healthcare provider.