About this Pregnancy Calculator
Pregnancy dating is usually expressed from the first day of the last menstrual period rather than from the day conception actually occurred. The Pregnancy Calculator in this script follows that convention.
It starts with the first day of the last menstrual period and an average cycle length, adds the standard 280-day pregnancy duration, and shifts the due date earlier or later when the average cycle is shorter or longer than 28 days.
It can also calculate how many pregnancy days and completed weeks have elapsed and how many days remain until the estimated due date. The page's reference tables place those dates within trimester ranges and common antenatal milestones.
The source is clear that the result is an estimate and that actual delivery can occur on a different date. This tool is therefore useful for organizing a pregnancy timeline and understanding gestational age, but it does not replace dating established by a clinician or ultrasound when those are available.
What Is a Pregnancy Calculator?
A Pregnancy Calculator estimates an expected due date and gestational age from menstrual-cycle information. The source uses EDD = LMP + 280 days + (Cycle Length − 28 days). Pregnancy Days are calculated as Current Date − LMP, completed Pregnancy Weeks as Floor(Pregnancy Days ÷ 7), and the remaining days as the remainder after division by seven.
Days Remaining are EDD − Current Date. The 280-day count corresponds to 40 weeks measured from the last menstrual period. A longer-than-28-day average cycle moves the estimate later, while a shorter cycle moves it earlier.
The calculation is a calendar estimate based on average cycle timing, not a direct measurement of conception or fetal development.
Reading Your Results
Your result will provide a primary Estimated Due Date. Remember that an EDD is an estimate, not a guarantee; full-term pregnancies safely deliver anywhere between 37 and 42 weeks.
The result also often details how far along you currently are, giving you immediate context for which trimester you are in and what developmental stage your baby has reached.
How to use this calculator
The calculator determines your estimated due date, current pregnancy week, and the days remaining until delivery.
1. Estimated Due Date (EDD)
Where
2. Pregnancy Age
3. Days Remaining Until Due Date
Note
The calculator assumes a normal pregnancy lasts 280 days (40 weeks).
If the menstrual cycle is longer than 28 days, the due date is moved later.
If the menstrual cycle is shorter than 28 days, the due date is moved earlier.
This provides an estimate only; the actual delivery date may vary.
Example 1 (28-Day Cycle)
Example 2 (30-Day Cycle)
Example 3
Result
12 weeks 0 days pregnant
Example 4
Pregnancy by Trimester
| Trimester | Weeks | Key Focus |
|---|---|---|
| First | 1 – 13 | Organ formation, highest miscarriage risk |
| Second | 14 – 27 | Growth, anatomy scan, movement felt |
| Third | 28 – 40 | Rapid weight gain, lung maturation |
Full term is 39 to 40 weeks; delivery before 37 weeks is considered preterm.
Recommended Weight Gain in Pregnancy
| Pre-Pregnancy BMI | Category | Recommended Total Gain |
|---|---|---|
| Under 18.5 | Underweight | 12.5 – 18 kg |
| 18.5 – 24.9 | Healthy weight | 11.5 – 16 kg |
| 25.0 – 29.9 | Overweight | 7 – 11.5 kg |
| 30.0 and above | Obese | 5 – 9 kg |
| Twin pregnancy (healthy BMI) | Multiple | 17 – 25 kg |
Based on Institute of Medicine guidance. Your doctor may advise differently for your situation.
Typical Antenatal Appointment Schedule
| Stage | Visit Frequency |
|---|---|
| Up to 28 weeks | Every 4 weeks |
| 28 – 36 weeks | Every 2 weeks |
| 36 weeks to birth | Every week |
| Dating scan | 8 – 14 weeks |
| Anatomy scan | 18 – 22 weeks |
| Glucose screening | 24 – 28 weeks |
Higher-risk pregnancies are usually monitored more frequently than this schedule.
Factors Affecting Your Pregnancy Result
The last-menstrual-period date is the anchor for every result, so uncertainty about that date changes the estimated due date and gestational age. Average cycle length is the second adjustment: the script assumes 28 days as the baseline and moves the due date by the difference between your average cycle and 28.
That adjustment still assumes a reasonably consistent relationship between cycle length and ovulation timing. Irregular cycles make an LMP-based estimate less dependable. The current date determines the displayed weeks completed and days remaining but does not change the underlying estimated due date.
The source's 280-day duration is a standard estimate, and the reference material notes that full term is around 39–40 weeks while actual delivery timing varies. The calculator does not incorporate ultrasound measurements, assisted-reproduction dates, medical history, multiple pregnancy, or clinical findings.
When a clinician supplies a revised dating estimate, that clinical date should not be replaced simply because the calendar formula gives a different result.
Benefits of Using the Pregnancy Calculator
- Estimate a due date from the last menstrual period while adjusting the source's 28-day baseline for your average cycle length.
- Convert elapsed pregnancy days into completed weeks and remaining days without manually counting across calendar months.
- See how much time remains until the estimated due date using the same date basis as the gestational-age calculation.
- Place the estimate alongside trimester and antenatal milestone references already included in the page.
- Use one consistent calendar method for planning while keeping the source's warning that actual delivery timing can vary.
Frequently asked questions
How does the calculator estimate the due date?
The source uses LMP + 280 days + (Cycle Length − 28 days). The cycle adjustment moves the estimate later for longer average cycles and earlier for shorter ones.
Why is pregnancy counted from the last menstrual period?
That is the dating convention represented in the source formula. It produces a gestational age that is typically about two weeks ahead of fetal age in a standard cycle.
How are pregnancy weeks calculated?
The script subtracts LMP from the current date to get pregnancy days, divides by seven for completed weeks, and uses the remainder for additional days.
Is the estimated due date the exact delivery date?
No. The source explicitly describes it as an estimate and notes that actual delivery may vary.
What if my cycle is irregular?
The formula relies on an average cycle length, so irregular timing reduces the usefulness of a simple LMP-based adjustment. The page does not model the other clinical information used for pregnancy dating.
Final Words
The strongest takeaway from the Pregnancy Calculator comes from using it to estimate a due date from the last menstrual period while adjusting the source's 28-day baseline for your average cycle length.
A key point is that the last-menstrual-period date is the anchor for every result, so uncertainty about that date changes the estimated due date and gestational age. For context, convert elapsed pregnancy days into completed weeks and remaining days without manually counting across calendar months.
When the assumptions change, a new Pregnancy Calculator result is more meaningful than an old number carried into a different scenario.
Disclaimer
This calculator provides estimates for general informational and educational purposes only and should not be treated as financial, medical, legal, or professional advice. Results depend entirely on the accuracy of the figures you enter.
Always verify important decisions with a qualified professional, official documentation, or your financial institution before acting on any result shown here.
Related Calculators
Body Mass Index calculator to determine if your weight is within healthy ranges based on height and weight measurements. Get BMI classification, health recommendations, and ideal weight ranges with detailed explanations of BMI categories and health implications.
Use CalculatorDaily calorie requirement calculator based on age, gender, weight, height, and activity level using proven metabolic formulas. Plan your diet, weight loss, or weight gain goals with personalized calorie recommendations and nutritional guidance for optimal health.
Use CalculatorCalculate Total Daily Energy Expenditure including BMR and activity level for calorie planning.
Use CalculatorCalculate your Basal Metabolic Rate (BMR) to determine daily calorie needs for weight management, fitness goals, and optimal nutrition planning.
Use CalculatorDetermine body type (ectomorph, mesomorph, endomorph) for personalized fitness and nutrition plans.
Use CalculatorCalculate daily macronutrient requirements (protein, carbs, fats) for fitness and nutrition goals.
Use CalculatorCalculate body fat percentage using US Army standards and measurements for fitness assessments.
Use CalculatorCalculate your body fat percentage using various measurement methods including skinfold, bioelectrical impedance, and body measurements for accurate fitness assessment.
Use CalculatorDetermine your ideal body weight based on height, age, gender, and body frame using multiple scientific formulas for healthy weight targets.
Use Calculator