Conception & Due Date Calculator
Choose the date you already know, and this tool will estimate your conception date and due date.
Important: This calculator gives estimates only. Your healthcare professional may adjust dates based on ultrasound and clinical findings.
How this date of conception and due date calculator works
This pregnancy calculator uses standard obstetric dating methods. In most pregnancies, due date is estimated as 280 days (40 weeks) from the first day of your last menstrual period (LMP). Conception usually occurs around ovulation, which is commonly about 14 days before the next period in a 28-day cycle.
Because every cycle is different, your results are an estimate, not a diagnosis. Early ultrasound measurements are often the most accurate way to confirm gestational age.
What each input means
1) Last menstrual period (LMP)
If you know the first day of your last period, this is usually the best starting point for at-home calculation. The tool will estimate:
- Your due date (LMP + 280 days)
- Your likely conception date (based on cycle length)
- Fertile window around estimated ovulation
2) Conception date
If you know approximately when conception happened, the tool calculates your estimated due date as conception date + 266 days (38 weeks). It will also estimate your likely LMP date for context.
3) Due date
If your provider already gave you a due date, this mode works backward to estimate conception date and LMP date.
Understanding the formulas
Most due date tools rely on simple date arithmetic:
- Due date from LMP: LMP + 280 days
- Conception from LMP: LMP + (cycle length - 14 days)
- Due date from conception: Conception + 266 days
- LMP from due date: Due date - 280 days
These formulas reflect average physiology. If you ovulate earlier or later than average, your actual conception date may shift.
Why your doctor may change your due date
It is common for due dates to be revised, especially after first-trimester ultrasound. This can happen when:
- Your cycles are irregular
- You were unsure of your exact LMP date
- Ovulation occurred earlier or later than expected
- Ultrasound growth measurements suggest a different gestational age
A changed due date does not necessarily mean anything is wrong. It often means the dating has become more accurate.
Quick planning checklist after you calculate
- Schedule your first prenatal visit
- Start or continue prenatal vitamins (folic acid is important)
- Review medications with your healthcare provider
- Track key milestones by trimester
- Discuss nutrition, exercise, and screening options
Frequently asked questions
Is conception date the same as pregnancy start date?
Not in medical dating. Clinicians usually count pregnancy from LMP, which is about 2 weeks before conception in a typical cycle.
Can this calculator tell me the exact day I got pregnant?
No. It can only estimate. Sperm can live in the reproductive tract for several days, and ovulation timing varies.
What if I conceived through IVF?
IVF pregnancies are often dated using embryo transfer details, which can be more precise than LMP-based formulas. Use your clinic's dates as primary guidance.
Medical note
This tool is for educational use and planning only. For personalized prenatal care, always follow your obstetrician, midwife, or fertility specialist.