Estimate your due date and track your pregnancy progress from your last menstrual period.
days
Estimated Due Date
Thursday, December 10, 2026
50% complete
Gestational Age20 weeks, 0 days
Current TrimesterSecond
Days Remaining139
Conception EstimateThursday, March 19, 2026
Due date is estimated at 280 days from LMP, adjusted by your cycle length. This is an estimate only; ultrasound dating may be more accurate. Always consult your healthcare provider for personalized advice.
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What is the Pregnancy Calculator?
A pregnancy calculator estimates your baby's due date and tracks your pregnancy progress. It uses your last menstrual period (LMP) and average cycle length to calculate a standard 280-day gestation period, adjusted for your cycle. The calculator shows your current gestational age in weeks and days, which trimester you are in, the estimated conception date, and days remaining until due date. It is important to note that the due date is an estimate; ultrasound measurements during your first trimester are typically more accurate.
How it works
The calculator takes your last menstrual period date and average cycle length as inputs. Pregnancy is typically counted from the first day of your last period (not conception). A standard pregnancy lasts 280 days (40 weeks) from LMP for a 28-day cycle; this adjusts automatically if your cycle is shorter or longer. The calculator then computes your gestational age today, your trimester, and the estimated due date by adding the adjusted gestation period to your LMP date.
Due Date = LMP + (280 + (cycle length − 28)) days; Gestational Age = (Today − LMP) ÷ 7 weeks
LMP is your last menstrual period date. Gestation is 280 days for a 28-day cycle, adjusted by the difference in your cycle length. For example, a 32-day cycle adds 4 days to the 280-day baseline. Gestational age is the elapsed time since LMP, divided by 7 to get weeks and days. The conception date is estimated at 14 days after LMP (typical ovulation timing).
Examples
Input
Result
Notes
LMP: January 15, 2024 | Cycle: 28 days
Due Date: October 22, 2024 | Gestational Age (today): varies | Conception: January 29, 2024
A standard 28-day cycle pregnancy with typical dating shows due date around week 40 from LMP.
LMP: December 1, 2023 | Cycle: 32 days
Due Date: September 13, 2024 | Adjusted by +4 days for longer cycle
Longer cycles shift the due date forward; shorter cycles move it back. The adjustment accounts for later ovulation.
LMP: March 10, 2024 | Cycle: 26 days
Due Date: December 13, 2024 | Adjusted by −2 days for shorter cycle
Shorter cycles indicate earlier ovulation, so due date is earlier than standard 280-day estimate.
How to use the Pregnancy Calculator
Enter the date of the first day of your last menstrual period (LMP) in the date field.
Enter your average menstrual cycle length (typically 21–35 days; 28 days is the average).
The calculator automatically computes your estimated due date, gestational age in weeks and days, your current trimester, and days remaining.
Note your estimated conception date (calculated as LMP + 14 days) for reference.
Remember that this is an estimate; your healthcare provider may adjust the due date based on ultrasound or other clinical findings.
Use the estimated due date for planning appointments, leave, and preparation, but confirm with your doctor.
Benefits
Quick due date estimate: Know your approximate due date in seconds without a doctor visit.
Trimester tracking: See which trimester you're in (first, second, or third) to monitor pregnancy milestones.
Cycle-length adjustment: Automatically accounts for your unique cycle to refine the estimate.
Conception estimate: Useful for dating the pregnancy and understanding development stages.
Progress tracking: See exactly how many weeks along you are and how many days remain.
Preparation planning: Use the due date to schedule maternity leave, arrange childcare, and prepare your home.
Tips & common mistakes
Common mistakes
Using last period date instead of first day: Always use the first day of your last period, not the last day, for accurate dating.
Ignoring cycle length variations: A 32-day cycle is common; using 28 days could shift your due date by several days.
Trusting the estimate completely: The due date is ±2 weeks; ultrasound in the first trimester is more accurate.
Not consulting a healthcare provider: Estimate your due date with this tool, but always confirm with your doctor or midwife.
Tips
Confirm with ultrasound: First-trimester ultrasound (8–13 weeks) can refine your due date within 3–5 days accuracy.
Track cycle length: Know your average cycle from your menstrual history; if unsure, use 28 days.
Adjust for irregular cycles: If your cycles vary widely (e.g., 25–32 days), use the average or consult your healthcare provider.
Plan around due date, not exact date: Only 5% of babies arrive exactly on due date; expect a 2-week window (±1 week is normal).
Frequently asked questions
What is the difference between gestational age and fetal age?
Gestational age is counted from the first day of your last period and is what doctors use clinically. Fetal age (or fertilization age) is the age from conception, typically 2 weeks less than gestational age. This calculator uses gestational age, the standard in medical practice.
How accurate is a pregnancy calculator?
A pregnancy calculator is ±2 weeks accurate based on LMP, especially if you have regular 28-day cycles. First-trimester ultrasound refines the date to ±3–5 days. If your cycles are irregular or longer/shorter, the estimate can vary more; discuss with your healthcare provider.
Can I use this calculator if my cycle is irregular?
Yes, but use your average cycle length. If your cycles vary significantly (e.g., 21 to 35 days), the estimate may be less accurate. An early ultrasound is especially helpful in this case.
Why do doctors count from the last period, not conception?
The exact date of conception is usually unknown, but most women remember their last period. Since ovulation occurs around day 14 of a 28-day cycle, counting from LMP is a standard reference point accepted worldwide in obstetrics.
What if I do not remember my last period date?
If you do not know your LMP, an early ultrasound can estimate your due date. Your healthcare provider may also calculate it based on when you first felt movement (quickening, around 16–20 weeks) or other clinical signs.
Can due date change after the first ultrasound?
Yes, if your ultrasound measurements suggest a different date, your healthcare provider may adjust it. This is most common if your LMP was uncertain or your cycle is irregular. Adjustments are typical and normal.