Pregnancy Calculator – Due Date, Conception, IVF and Week-by-Week Pregnancy Tracking
This comprehensive Pregnancy Calculator helps you estimate your due date, probable conception date, trimester stage and gestational age using multiple methods. Whether you know the first day of your last menstrual period (LMP), an ovulation date, ultrasound measurements, an IVF transfer date or an already confirmed due date, this calculator gives you a complete, accurate timeline of your pregnancy. It also includes a built-in week-by-week tracker, allowing you to instantly see how far along you are at any moment.
Pregnancy calculations may seem simple on the surface, yet several variables affect estimated due dates and gestational age. Different medical providers may calculate slightly different timelines depending on the method used. That is why a multi-input tool like this is helpful. It brings all major approaches together in one place and gives clear, consistent results you can easily understand.
How This Pregnancy Calculator Works
The Pregnancy Calculator uses standard obstetric calculation methods based on global clinical guidelines. It supports six popular calculation inputs:
- LMP (Last Menstrual Period)
- Ovulation or Conception Date
- Ultrasound Measurements
- Known Due Date
- IVF Transfer Details (Day-3 or Day-5 Embryos)
- Week-by-Week Tracking
Each method calculates your due date and gestational age using medically recognized formulas. The default assumption for most pregnancies is a 280-day cycle from LMP to due date (40 weeks), or approximately 266 days from conception. IVF calculations adjust the starting point based on embryo development stage, making IVF due date estimation particularly precise.
Why Pregnancy Calculations Vary
Although pregnancy is often described as lasting 40 weeks, the exact definition of pregnancy length varies depending on the calculation method. Here is why the numbers differ:
- LMP-based calculations assume ovulation occurs 14 days before your expected period.
- Conception-based calculations assume pregnancy begins at ovulation, which shifts the timeline by two weeks compared to LMP.
- Ultrasound-based calculationsy on fetal developmental measurements, which offer better accuracy during early pregnancy.
- IVF calculations offer the most precise timeline because conception happens outside the body and embryo age is known.
These differences make it useful to switch between methods depending on your circumstances. For example, ultrasound estimates may be more accurate in early pregnancy if your cycles are irregular. IVF estimates are the most precise because embryo age and implantation timing are medically documented.
LMP-Based Pregnancy Calculation
The most common way to estimate pregnancy dates is by using the first day of your last menstrual period (LMP). This method is used by most doctors during the first prenatal visit. LMP-based pregnancy calculation assumes a 28-day cycle with ovulation on day fourteen. If your cycles are longer or shorter, this calculator adjusts the conception estimate accordingly.
Using LMP, your:
- Estimated ovulation date occurs roughly on cycle day 14
- Estimated conception date is around the ovulation window
- Estimated due date is LMP + 280 days (40 weeks)
This method is simple buties heavily on cycle accuracy. Women with irregular cycles may see slight variations compared to actual fetal age.
Ovulation or Conception-Based Calculation
If you know the exact date of ovulation or conception, this method gives a more precise timeline than LMP. Ovulation prediction kits, fertility charting or assisted reproduction procedures may provide accurate dates.
For conception-based calculations:
- Due date = Conception date + 266 days
- LMP is estimated by subtracting 14 days from conception
- Gestational age is calculated from the estimated LMP
This method is especially helpful if your cycle is irregular or if LMP is unknown.
Ultrasound-Based Pregnancy Calculation
Ultrasound dating is considered the most accurate method during the first trimester. Ultrasound measures fetal structures such as the crown-rump length (CRL), gestational sac size or fetal pole development. These measurements provide medically validated gestational ages with minimal margin of error.
With ultrasound-based calculations:
- You provide the date of the scan
- You enter the gestational age measured on that day
- The calculator estimates your due date and LMP based on fetal size
This method is recommended by doctors when LMP is uncertain or cycles are irregular.
IVF Pregnancy Calculation
IVF pregnancies follow a different calculation method because the exact fertilization and embryo development stages are known. Due date estimation depends on embryo age at the time of transfer.
For IVF:
- Day-3 embryo transfer adds 261 days to the transfer date
- Day-5 embryo transfer adds 259 days
These durations align IVF pregnancies with traditional gestation length. Because IVF timelines are precisely controlled, IVF due date estimates are typically the most accurate of all methods.
Known Due Date Basederse Calculation
If your doctor has already given you a due date, this tool canerse-calculate the estimated:
- Conception date
- LMP date
- Gestational age
- Trimester stage
This is helpful if you change clinics, get a second opinion or simply want a deeper understanding of your pregnancy timeline.
Week-by-Week Pregnancy Tracker
The built-in week-by-week tracker helps you see:
- Your current pregnancy week
- Your current month
- Your current trimester
- Your approximate pregnancy progress percentage
- Your estimated due date
This feature is especially helpful for planning appointments, prenatal vitamins, ultrasound schedules, weight tracking and monitoring trimester-specific milestones.
Understanding Gestational Age vs Fetal Age
Many people are surprised to learn that gestational age and fetal age are not the same. Understanding the difference can help you make sense of pregnancy calculations.
- Gestational age counts from the first day of the LMP
- Fetal age starts at conception, usually two weeks later
This is why someone only two weeks past ovulation is considered four weeks pregnant. Medical professionals almost always use gestational age for consistency.
Trimester Breakdown
Pregnancy is divided into three major trimesters, each representing a distinct stage of fetal development and maternal changes.
- First trimester: Week 0 to 13 weeks 6 days
- Second trimester: Week 14 to 27 weeks 6 days
- Third trimester: Week 28 to birth
The Pregnancy Calculator automatically identifies your trimester based on your gestational age and provides clear trimester progress updates.
How Accurate Is a Pregnancy Calculator?
A pregnancy calculator provides accurate estimates based on mathematical models and widely accepted medical rules. However, real-life pregnancies vary. Only 4 percent of babies are born exactly on their due date. Most births happen within a two-week window before or after the estimated due date.
This tool gives you a medically aligned estimate, but regular prenatal care is essential for precise guidance and monitoring.
Factors That Can Affect Pregnancy Timing
Several biological and medical factors can influence gestational age, fetal growth and the actual delivery date. These include:
- Cycle length irregularities
- Delayed or early ovulation
- Implantation timing
- Medical conditions such as PCOS
- Multiple pregnancies (twins, triplets)
- Maternal age
- IVF embryo development stage
- Placental factors
- Lifestyle and health conditions
For the most accurate dating, doctors ofteny on a combination of LMP, ultrasound and ongoing clinical assessment.
Why Use an All-in-One Pregnancy Calculator?
Most online pregnancy calculators only support one method of calculation. This tool combines every recognized approach, giving you flexibility depending on what information you have available.
You might choose:
- LMP-based estimation early in pregnancy
- Ultrasound-based calculation after a scan
- IVF calculation if you underwent assisted reproduction
- Due-date-basederse calculation when switching clinics
- Week-by-week tracking throughout pregnancy
This single tool adapts to your entire pregnancy timeline without needing multiple calculators.
Related Tools You May Find Useful
Here are additional tools on MyTimeCalculator that complement pregnancy planning:
- Ovulation Calculator for predicting fertile windows
- Due Date Calculator for a simplified version of this tool
- BMI Calculator to monitor healthy pregnancy weight gain
- Date Calculator for calculating weeks and days between important pregnancy milestones
Important Disclaimer
This Pregnancy Calculator is for educational and informational purposes only. It does not replace professional medical advice, diagnosis or prenatal care. Always consult your doctor, midwife or healthcare provider for personalized guidance, medical evaluations and pregnancy-related decisions.
Pregnancy FAQs
Frequently Asked Questions Pregnancy Calculators
Find clear answers to common questions due dates, conception timing, IVF calculations and gestational age.
This calculator follows standard medical formulas for estimating due date and gestational age. While accurate for planning, only 4 percent of babies are born exactly on their estimated due date. Always use prenatal care for precise monitoring.
The conception date shown is an estimate unless you know the exact ovulation or IVF transfer date. Natural conception can occur within a fertile window of several days.
Ultrasound measurements during early pregnancy offer the most precise estimation of gestational age. If ultrasound measurements differ significantly from LMP calculations, doctors may update your due date accordingly.
Yes. IVF dates are generally more accurate because embryo development stage and transfer timing are known precisely. This removes much of the uncertainty associated with natural conception.
Irregular cycles can make LMP-based calculations less accurate. In these cases, ovulation tracking or ultrasound measurements are moreiable. The calculator allows you to switch between methods easily.
The tracker uses your LMP or known due date to determine the total number of days since pregnancy began. It then converts those days into weeks and days to show your current gestational age.
Yes. Enter your doctor-confirmed due date into the Conception & Due Date method. The calculator will then recalculate your pregnancy timeline based on that due date.
This tool calculates pregnancy timelines using standard single-baby gestation formulas. Twin and multiple pregnancies often follow slightly different growth and delivery timelines. Consult your doctor for personalized guidance.
Healthcare providers use LMP because it offers a consistent, measurable starting point. Ovulation and conception vary from woman to woman and cycle to cycle, making LMP the mostiable universal baseline.
No. A due date is an estimate, not a prediction. Most babies arrive within a window of two weeks before or after the calculated due date.