Pregnancy Due Date Calculator
Pregnancy Timeline & Milestones
Key developmental milestones by week
| Week | Trimester | Milestone |
|---|---|---|
| Week 4 | 1st | Positive pregnancy test possible |
| Week 6 | 1st | Heartbeat detectable on ultrasound |
| Week 8 | 1st | First prenatal visit typically scheduled |
| Week 12 | 1st | End of first trimester; risk of miscarriage drops |
| Week 16 | 2nd | Gender may be visible on ultrasound |
| Week 20 | 2nd | Anatomy scan; halfway point |
| Week 24 | 2nd | Viability milestone |
| Week 28 | 3rd | Third trimester begins |
| Week 36 | 3rd | Baby is considered early term |
| Week 37 | 3rd | Full term begins |
| Week 40 | 3rd | Estimated due date |
How We Calculate This
This pregnancy due date calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
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The pregnancy due date calculator uses Naegele's Rule, the standard medical method for estimating delivery dates.
The basic rule:
- From LMP: Add 280 days (40 weeks) to the first day of your last menstrual period
- From Conception: Add 266 days (38 weeks) to the conception date
- Naegele's Rule assumes a 28-day menstrual cycle with ovulation on day 14
- Only about 5% of babies are born on their exact due date — most arrive within 2 weeks before or after
This calculator provides an estimate. Your healthcare provider may adjust your due date based on ultrasound measurements, especially in the first trimester, which can be more accurate than date-based calculations.
When Would You Use This Calculator?
This pregnancy due date calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How accurate is a due date calculator?
Due date calculators are estimates. Only about 5% of babies are born on their exact due date. About 80% are born between 37 and 42 weeks. First-trimester ultrasound dating is generally more accurate, with a margin of error of about 5-7 days.
What is Naegele's Rule?
Naegele's Rule is the standard formula used since the 1800s: take the first day of the last menstrual period, add one year, subtract three months, and add seven days. This equals 280 days (40 weeks) from the LMP.
What if my cycle is longer or shorter than 28 days?
If your cycle is longer than 28 days, your due date may be slightly later. If shorter, slightly earlier. For each day your cycle differs from 28 days, adjust your due date by that many days. Your doctor can help refine this.
What are the trimesters?
First trimester: weeks 1-12. Second trimester: weeks 13-27. Third trimester: weeks 28-40. Each trimester has different developmental milestones and physical changes.
When should I tell my doctor my due date?
Share your LMP date and this calculated due date at your first prenatal appointment (typically around 8-10 weeks). Your doctor will likely confirm or adjust this date based on an early ultrasound measurement.