Predict next period, fertile window and ovulation day from LMP and cycle length with a 3-cycle calendar view. Your entries remain private on this device.
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Quick answer: Period & Ovulation Calculator — Next period + fertile window Free, no signup, runs in your browser. See below for the interactive tool, 4-step guide and FAQs.
Average cycle, typically 28 days (20–45)
Enter your last menstrual period date to calculate the next period.
Average cycle, typically 28 days (20–45)
Enter your last menstrual period date to calculate ovulation.
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Next span equals last period and mean cycle span, with ovulation near and cycle minus fourteen. September first 2026 with twenty-eight days gives next September twenty-ninth and ovulation near September fifteenth. Three-view math runs on-device offline, unsent. See /terms for scope.
Period prediction is general information only, never diagnostic triage for amenorrhea or bleeding disorders. Stress, travel, illness, and perimenopause shift timing by days. Thirty-five-day cycle after stress is normal variation, but missed periods need testing. Consult clinician for concerns and see /terms for details.
Three-cycle calendar assumes average length holds steady, so swings over seven days make predictions wobble. Twenty-four then thirty-two-day cycles shift September twenty-ninth by days and blur fertile September tenth to sixteenth. Log three months, use averages cautiously; general information only, and see /terms.
Soaking pad hourly for two hours, periods exceeding seven days, intermenstrual spotting, or missed three months merit workup. September first with twenty-eight-day regularity turning to forty-five-day gaps suggests anovulation or thyroid shift. Tracking flow heaviness, pain scores, and clots equips clinician triage efficiently.
Premenstrual cramping, breast tenderness, and mood shifts overlap early gestation, confusing symptom reading. September fifteenth ovulation and fourteen days gives September twenty-ninth test date; testing before missed menses risks false negatives. Waiting until day thirty with first-morning urine improves accuracy. Clinician confirmation follows positive results.
Next period equals last period and average cycle, with ovulation near and cycle minus fourteen for context. September first 2026 with twenty-eight days gives next September twenty-ninth, ovulation September fifteenth, fertile September tenth to sixteenth. Three-cycle view previews October twenty-seventh and November twenty-fourth. Forecast table shows horizon clearly | Cycle start | Length average | Predicted next | Following period | Sep 1, 28 days | Sep 29 | Oct 27 | Sep 1, 32 days | Oct 3 | Nov 4 | Oct 1, 28 days | Oct 29 | Nov 26. Edge case of anovulatory breakthrough mislabels start inaccurately. Limitation assumes median stability without shifts. Five-day bleeds are assumed for calendar shading and planning all offline private with no upload. This is general information only, not medical advice. See /terms.
Enter last period and twenty-one to thirty-five-day average and three to seven-day bleed; tool draws three months instantly. If cycles swing over seven days, September twenty-ninth may land plus-minus four days and fertile hints blur. Stress, travel, and perimenopause add noise entirely offline with no upload. Second example at thirty-two-day average shifts next to October third with fertile late September. Variability table guides caution methodically | Swing range | Accuracy window | Guidance action | Under 4 days | plus-minus 2 days | calendar reliable alone | Over 7 days | plus-minus 5 days | add ovulation kits. Edge case of postpartum lactation suppresses cycling unpredictably for months. Limitation excludes hormonal pathology and thyroid disease. Log three cycles, use median length, treat fertile days as context only, all offline private. This is general information only, not medical advice. See /terms.
Pick September first, twenty-eight days, five-day bleed with September twenty-ninth next, October twenty-seventh after, ovulation September fifteenth with shading. Do not use for contraception since ovulation varies across months by days with sperm survival. Log three months, use median length, treat fertile hints cautiously offline private with backup. Test October third start for October thirty-first next to scale intuition across months. Verify fertile September tenth to sixteenth for context only with calendar. Edge case of emergency contraception and illness resets cycle baseline entirely. Limitation covers prediction only, excluding diagnosis for missed periods or bleeding disorders. This period prediction is general information only, so see /terms and ask clinician for worries. For conception timing, switch to the Ovulation tab above in this same tool for private math and a three-cycle view.