Estimate due date, conception date and trimesters from last menstrual period and cycle length to see dates. Inputs stay on your device with local math.
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Quick answer: Pregnancy Calculator — Due date & trimesters 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 due date.
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Naegele adds 280 days and cycle minus twenty-eight, with conception near last period and fourteen days. January first 2026 with twenty-eight-day cycle gives due October eighth 2026 and conception near January fifteenth. Dates compute in-tab net-off with no file kept. See /terms for limits.
Pregnancy estimate is general information only, never diagnostic dating for care decisions. Irregular cycles, IVF dates, and early ultrasounds change dating substantially. Thirty-two-day cycle pushes ovulation later than day fourteen. Confirm timing with clinician and ultrasound and see /terms for details.
Regular twenty-eight-day cycle and average ovulation on day fourteen are assumed, so irregular ovulation, missed periods, and IVF transfers shift by days or weeks. January first gives October eighth, but thirty-five-day cycle adds about a week. Use trimester cutoffs only for planning; general information only and see /terms.
First-trimester crown-rump length within eight weeks predicts delivery within plus-minus five days, outperforming period math when cycles vary. Discrepancy over seven days prompts revised due date from sonographer. Combining January first period estimate of October eighth with 8-week scan sharpens planning. Always follow obstetrician assignment for care.
First trimester hosts nuchal translucency and cell-free DNA, second hosts anatomy scan near twenty weeks, third hosts growth and Group B strep. January first conception places first-trimester close near April eighth and second near July. Scheduling through provider portal ensures windows are met despite dating uncertainty.
Naegele estimates delivery as last period and 280 days and cycle minus twenty-eight, with conception near and fourteen for twenty-eight-day pattern and later for longer cycles. January first 2026 gives due October eighth 2026 and conception near January fifteenth. Thirty-two-day cycle pushes due to October twelfth with ovulation January nineteenth. Dating table shows variance clearly | LMP and cycle length | Conception date | Due date | Jan 1, 28 days | Jan 15 | Oct 8 | Jan 1, 32 days | Jan 19 | Oct 12 | Feb 10, 28 days | Feb 24 | Nov 17 | Mar 5, 35 days | Mar 19 | Dec 10. Edge case of irregular bleeding misidentifies start and skews weeks. Limitation assumes ovulation day fourteen uniformly. Trimesters split at weeks thirteen and twenty-seven for visit planning across forty weeks total. This is general information only, not medical advice. See /terms for details.
Enter last period from 2024 to 2027 and cycle twenty-one to thirty-five days; longer cycles add days to due date proportionally with luteal stability. Model assumes ovulation day fourteen, so late ovulation, irregular bleeding, and IVF transfer dates break math and require ultrasound correction. Early ultrasound within eight weeks beats period dating by plus-minus five days with crown-rump precision. Second example at thirty-five-day cycle adds seven days versus twenty-eight baseline with conception delayed. Variation table shows impact methodically | Cycle duration | Ovulation day | Due shift versus baseline | 28 days | day 14 | baseline Oct 8 | 32 days | day 18 | and 4 days | 35 days | day 21 | and 7 days. Edge case of anovulatory months voids estimate entirely. Limitation excludes luteal phase defects and bleeding misclassification. Tool shows conception, weeks today, trimester instantly privately offline. This is general information only, not medical advice. See /terms.
Pick January first 2026, twenty-eight-day cycle for due October eighth 2026, conception January fifteenth, now count weeks to plan scans and screening windows. If cycles vary over seven days or IVF was used, trust ultrasound over Naegele by five to seven days with sonographer assignment. Test February tenth for November seventeenth and March fifth for December tenth to scale intuition across calendar. Verify trimester cutoffs at thirteen and twenty-seven weeks for visit scheduling. Edge case of spotting mistaken for period shifts dating by weeks and confuses viability. Limitation covers planning only, excluding viability, complications, and multiple gestation for forty weeks. This pregnancy estimate is general information only, not medical advice, so see /terms and confirm with clinician promptly. For fertile timing use our period and ovulation calculator at /period-calculator free offline with private math and calendar.