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Period Calculator

Predict your next period, fertile window, and ovulation date

Enter your last period date to see predictions
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What is Period Calculator?

Track menstrual cycle and predict next period, fertile window, and ovulation date. Free online period and ovulation calculator. Health calculators aligned with Indian dietary guidelines and South Asian health benchmarks. TekPulse's Period Calculator is completely free — no signup, no ads in results, and no data stored on our servers.

How to Use Period Calculator Online

  1. Enter the start date of your last menstrual period
  2. Enter your average cycle length in days (typically 21–35 days; average is 28)
  3. Enter your average period duration in days
  4. View the predicted dates for your next 6 periods, ovulation windows, and fertile days
  5. Reminder: this is for planning purposes only and not a substitute for medical advice

Period Calculator Formula & Calculation

Next Period Start = Last Period Start + Cycle Length | Ovulation ≈ Next Period Start − 14 days | Fertile Window = Ovulation − 5 days to Ovulation + 1 day

This is a simple date-arithmetic predictor based on average cycle patterns: it assumes a consistent cycle length (user-entered, default 28 days) and that ovulation occurs roughly 14 days before the next period begins, which is the average luteal phase length — not a measurement of actual ovulation.

Example: Last period started 1 October, cycle length 28 days → Next period predicted for 29 October → Ovulation ≈ 15 October → Fertile window ≈ 10–16 October.

Key Factors That Affect Your Result

  1. Cycle regularity — The prediction assumes every cycle is the same length as entered; actual cycles commonly vary by several days even in people with regular periods, and more for those with irregular cycles, so treat dates as estimates rather than fixed appointments.
  2. Not a diagnostic or contraceptive tool — This calculator is for general awareness and planning only; it does not detect ovulation directly (which requires methods like basal body temperature tracking or ovulation test kits) and should not be relied on for contraception.
  3. Luteal phase assumption — The 14-day gap between ovulation and the next period is a population average; actual luteal phase length varies by individual (commonly 10–16 days), which shifts the true ovulation date relative to the estimate.

Why Use TekPulse Period Calculator?

Runs Entirely in Your Browser
Predictions are calculated from your dates using JavaScript — your cycle data is never uploaded or stored
Date-Based Cycle Prediction
Projects your next 3 periods, fertile window, and ovulation day using simple calendar math from your cycle length
Ovulation Estimated at Day 14
Ovulation is estimated using the standard 14-days-before-next-period rule, not a diagnostic or medical calculation
Informational Estimate Only
A simple average-cycle predictor meant for planning, not a substitute for medical tracking or advice

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Frequently Asked Questions

The predictions are based on your average cycle length (typically 28 days). Accuracy varies — stress, illness, diet changes, and hormonal factors can shift cycles by several days. The tool is for informational guidance, not medical diagnosis.

Enter the first day of your last period and your average cycle length. Add your cycle length to the start date to find the next period date. For example: last period = June 1, cycle = 28 days → next period = June 29.

The fertile window typically spans 5 days before ovulation and 1 day after. Ovulation occurs approximately 14 days before your next period (cycle length − 14). For a 28-day cycle, ovulation is around day 14.

The luteal phase is the second half of your menstrual cycle, from ovulation until your next period begins. It typically lasts 12–16 days. If fertilization does not occur, progesterone drops and menstruation begins.

Yes — our tool shows the next 3 cycle predictions including period dates, fertile windows, and ovulation dates for each upcoming cycle, so you can plan ahead for weeks.

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