Pregnancy Calculator
Track your pregnancy progress by week and day. Calculate current trimester, estimated fetal growth, and key milestone dates.
Key Features
- •Current week and day of pregnancy (0-40 weeks)
- •Trimester tracking (First: 1-13, Second: 14-27, Third: 28-40)
- •Estimated fetal weight and length (percentile-based)
- •Milestone reminders (ultrasounds, screenings, vaccines)
- •Weekly development summaries (key organ development)
- •Due date countdown (days remaining)
- •Days pregnant counter (conceptual age)
- •Pregnancy weight gain tracker (by week)
- •Kick count log (third trimester)
- •Printable pregnancy timeline
About Pregnancy Calculator
Pregnancy is a journey of approximately 280 days (40 weeks) from the first day of your last menstrual period (LMP) to delivery. Our Pregnancy Calculator helps you navigate this journey by providing week-by-week insights: current gestational age, trimester status, estimated fetal development milestones, and important appointment dates.
How Pregnancy Dating Works
Healthcare providers typically date pregnancy from the first day of your Last Menstrual Period (LMP), which is approximately 2 weeks before actual conception. This means:
- LMP-based gestational age: Conception assumed at 2 weeks
- Actual fetal age: Approximately 2 weeks less than gestational age
- Due date: 40 weeks from LMP (38 weeks from conception)
Calculation Methods:
Method 1: LMP (Last Menstrual Period) - Standard Clinical Method
The most common method, assuming a regular 28-day cycle with ovulation on day 14.
- Enter date of your LMP
- Calculator adds 280 days (40 weeks)
- Result: Estimated Due Date (EDD)
Method 2: Conception Date - For Known Conception (IVF, artificial insemination)
- Enter date of conception (e.g., IVF transfer date minus 2 days for day 3 embryo, minus 5 days for day 5 blastocyst)
- Calculator adds 266 days (38 weeks)
Method 3: Ultrasound Dating - Most Accurate
If you have an early ultrasound (8-12 weeks), use the crown-rump length (CRL) to determine gestational age. Our calculator works backwards from due date provided by your provider.
Trimester Breakdown: What to Expect
| Trimester | Weeks | Key Developments | Symptoms |
|---|---|---|---|
| First | 1-13 | Neural tube closes (week 6), heart beats (week 6-7), all major organs form | Morning sickness, fatigue, breast tenderness, frequent urination |
| Second | 14-27 | Movement felt (18-22 weeks), hearing develops (week 18), responds to sound | Energy returns, belly grows, back pain may begin |
| Third | 28-40 | Lungs mature (week 36), turns head-down (weeks 32-36), gains 1/2 lb per week | Shortness of breath, swelling, Braxton Hicks, sleep disruption |
Week-by-Week Fetal Development Highlights
- Week 4: Implantation. Pregnancy test positive.
- Week 6: Heartbeat detected on ultrasound.
- Week 8: Baby is now a fetus. All essential organs present.
- Week 12: Risk of miscarriage drops significantly. Nuchal translucency screening.
- Week 16: Sex organs visible on ultrasound.
- Week 20: Anatomy scan. You may feel first movements (quickening).
- Week 24: Viability (25-50% survival if born now with NICU).
- Week 28: Third trimester begins. Baby opens eyes.
- Week 32: Baby turns head down in most cases.
- Week 36: Lungs mature. Braxton Hicks intensify.
- Week 37-40: Full term. Baby could arrive any day.
- Week 41-42: Post-term. Induction often recommended.
Important Milestone Dates Your Calculator Provides
| Milestone | Timing | What Happens |
|---|---|---|
| Positive pregnancy test | Week 4 | hCG detectable |
| First heartbeat | Week 6-7 | Ultrasound confirmation |
| Nuchal Translucency scan | Week 11-13 | First trimester screening |
| Anatomy scan | Week 18-22 | Detailed organ check, sex reveal |
| Glucose tolerance test | Week 24-28 | Gestational diabetes screening |
| Tdap vaccine | Week 27-36 | Whooping cough protection |
| GBS swab | Week 36 | Group B Strep test |
| Cervical check | Week 37+ | Check dilation/effacement |
Due Date Probability Distribution
Only 5% of babies are born on their exact due date. The actual delivery window:
- 37 weeks: "Early term" (10% of births)
- 38 weeks: 15%
- 39 weeks: 20% (most common single week)
- 40 weeks (due date): 5% (only!)
- 41 weeks: 15%
- 42 weeks: 5%
First-time moms (nulliparas) average 5-7 days past due date. Moms who've given birth before (multiparas) average 2-4 days past due.
Pregnancy Weight Gain Recommendations (IOM Guidelines)
| Pre-pregnancy BMI | Recommended Total Gain | Rate in 2nd/3rd Trimester |
|---|---|---|
| Underweight (<18.5) | 28-40 lbs (13-18 kg) | 1.0-1.3 lbs/week |
| Normal (18.5-24.9) | 25-35 lbs (11-16 kg) | 0.8-1.0 lbs/week |
| Overweight (25-29.9) | 15-25 lbs (7-11 kg) | 0.5-0.7 lbs/week |
| Obese (30+) | 11-20 lbs (5-9 kg) | 0.4-0.6 lbs/week |
Weight gain is minimal (2-5 lbs) in first trimester, then accelerates.
FAQ: Pregnancy Calculator
My cycles are irregular (not 28 days). How do I adjust?
If your cycles are consistently longer or shorter, adjust the calculator by the difference. For 35-day cycles (7 days longer): subtract 7 days from the LMP-based due date. For 21-day cycles (7 days shorter): add 7 days. Discuss with your provider.
What if I conceived using IVF?
Use the conception date method. For Day 5 blastocyst transfer, conception = transfer date minus 5 days. Some clinics provide an "adjusted LMP" date equals transfer date minus 19 days (for Day 5).
Why do doctors change my due date after ultrasound?
Early ultrasound (8-12 weeks) measures crown-rump length (CRL) which accurately predicts gestational age within 3-5 days. If there's a discrepancy >5 days from LMP dates, providers use ultrasound dates (more accurate for dating).
What is a "late period" vs "pregnancy"?
A period is considered late after 5-7 days beyond your usual cycle length. However, ovulation can vary. Use our calculator with your LMP, but confirm pregnancy with a test. If there's no period by week 6-7, see your provider.
Pregnancy Calculator is optimized for fast browser-based use, so you can test multiple scenarios in seconds.
Formula & Logic
- 01Gestational age from LMP: Current weeks = (Today's Date - LMP Date) ÷ 7 days.
- 02Due Date (Naegele's Rule): LMP date + 280 days (40 weeks).
- 03Due Date from Conception: Conception date + 266 days (38 weeks).
- 04Trimester boundaries: First = weeks 0-13, Second = weeks 14-27, Third = weeks 28-40.
- 05Fetal size estimates based on Hadlock growth curves (percentile by gestational week).
Practical Examples
- 01Baseline check: Use realistic inputs in Pregnancy Calculator to generate a first-pass estimate.
- 02Sensitivity check: Change one key input at a time to compare how the output shifts.
- 03Decision check: Save two or more scenarios and use the differences to choose the better option.
Important Limitations
- •Results depend on the accuracy of your inputs.
- •Displayed values may be rounded for readability.
- •Health-related outputs are educational estimates and should not replace medical advice.
Frequently Asked Questions
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