Anatomy Scan Date Calculator

Enter the date of your last menstrual period (LMP) to instantly find your 20-week anatomy scan window, ideal appointment date, and estimated due date.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter LMP Month
Input the month (1-12) your last menstrual period (LMP) began. For example, enter 10 for October.
2
Enter LMP Day
Enter the calendar day your last menstrual period began. For example, enter 26.
3
Enter LMP Year
Input the four-digit year your last menstrual period began. For example, enter 2024.
4
Review your results
The calculator will display your ideal anatomy scan date, the full scan window, current pregnancy age, scan window status, and estimated due date.

Example Calculation

A pregnant person whose last menstrual period began on October 26, 2024, needs to find their ideal anatomy scan date and overall scan window.

LMP Month

LMP Day

LMP Year

2024

Results

March 15, 2025

Tips

Confirm Your LMP Date

The accuracy of all calculated dates relies heavily on the correct Last Menstrual Period (LMP) date. If your cycles are irregular or you're unsure, an early ultrasound (before 12 weeks) can provide a more precise estimated due date.

Schedule Early

Once your scan window opens, schedule your anatomy scan promptly. Clinics can book up quickly, and attending within the ideal 18–22 week window ensures the best visualization for fetal development assessment.

Prepare for the Scan

Some clinics recommend drinking plenty of water before your anatomy scan to ensure a full bladder, which can improve imaging quality. Also, be prepared with any questions you have for the sonographer or healthcare provider regarding the baby's development.

Pinpointing Your Pregnancy Anatomy Scan Dates

The Anatomy Scan Date Calculator helps expectant parents determine their essential 18–22 week anatomy scan window, the ideal appointment date, and their current pregnancy age, all from the date of their last menstrual period (LMP). This tool is critical for timely scheduling of one of the most comprehensive prenatal assessments. During this period, the baby's organs and growth can be thoroughly examined, with approximately 2-3% of pregnancies revealing a significant anomaly. Accurate timing ensures optimal visualization for this important milestone in 2025.

The Significance of Mid-Pregnancy Scans

The mid-pregnancy anatomy scan is a cornerstone of prenatal care, offering a detailed look at fetal development that is unmatched by earlier ultrasounds. This scan's primary purpose is to assess the baby's organ development, growth, and overall structure, identifying any potential issues early. For example, it meticulously checks the heart's four chambers, the brain's hemispheres, the spine's alignment, and the kidneys' formation. It also determines the placental location, which is crucial for delivery planning. The 18-22 week window is optimal because the fetus is large enough for detailed assessment, yet there is still ample amniotic fluid for clear imaging. Detecting an anomaly during this scan can lead to early intervention or specialized care, significantly impacting outcomes.

Calculating Key Pregnancy Milestones

The Anatomy Scan Date Calculator uses your Last Menstrual Period (LMP) as the starting point to calculate several key pregnancy dates. The core logic is based on standard gestational periods.

First, it establishes your LMP date:

LMP Date = new Date(LMP Year, LMP Month - 1, LMP Day)

Then, it calculates critical dates by adding specific numbers of days to the LMP:

Scan Window Start = LMP Date + 126 days (18 weeks)
Ideal Scan Date = LMP Date + 140 days (20 weeks)
Scan Window End = LMP Date + 154 days (22 weeks)
Estimated Due Date = LMP Date + 280 days (40 weeks)

The current pregnancy age is determined by calculating the days elapsed between your LMP and today's date, then converting this to weeks and days. This provides a clear roadmap for your pregnancy journey.

💡 If you're still in the planning stages of your family, our Peak Fertility Day Calculator can help pinpoint optimal times for conception.

Finding Scan Dates for an October 2024 LMP

Let's calculate the key dates for a pregnant person whose last menstrual period began on October 26, 2024:

Establish LMP: October 26, 2024.
Calculate Scan Window Opens (18 weeks):
- Add 126 days to October 26, 2024.
- This falls on March 1, 2025.
Calculate Ideal Scan Date (20 weeks):
- Add 140 days to October 26, 2024.
- This falls on March 15, 2025.
Calculate Scan Window Closes (22 weeks):
- Add 154 days to October 26, 2024.
- This falls on March 29, 2025.
Calculate Estimated Due Date (40 weeks):
- Add 280 days to October 26, 2024.
- This falls on August 2, 2025.
Current Pregnancy Age (if today is Oct 26, 2024):
- 0 weeks, 0 days.

The primary result, the Ideal Scan Date, is March 15, 2025. This provides a clear target for scheduling the comprehensive fetal anatomy scan.

💡 For those with irregular cycles, our PCOS Cycle Length Estimator can offer insights into menstrual patterns that might affect LMP accuracy.

The Significance of Mid-Pregnancy Scans

What Sonographers Look For During an Anatomy Scan

During the 18-22 week anatomy scan, sonographers and radiologists meticulously examine a wide array of fetal structures and measurements to ensure healthy development. Key assessments include fetal biometry, which involves measuring the head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL) to estimate growth and weight, comparing them against CDC growth charts. They also perform a detailed survey of all major organ systems: checking for the presence and proper formation of the four chambers of the heart, the brain's hemispheres and cerebellum, the spine's integrity, and the kidneys and bladder. The placental position is also confirmed, noting if it's low-lying or previa. A "normal" finding indicates that all visible structures appear to be developing as expected, providing reassurance to expectant parents and their healthcare providers.

Frequently Asked Questions

What is an anatomy scan during pregnancy?

An anatomy scan, also known as a mid-pregnancy ultrasound or level 2 ultrasound, is a detailed ultrasound examination performed around the middle of pregnancy to assess the baby's growth, development, and organ systems. It checks for structural abnormalities, confirms the baby's position, and determines the location of the placenta. This comprehensive scan provides crucial information about the baby's health and well-being, typically occurring between 18 and 22 weeks of gestation.

Why is the 18–22 week window ideal for an anatomy scan?

The 18–22 week window is considered ideal for an anatomy scan because at this stage, the baby is large enough for detailed visualization of its organs and structures, but still has enough amniotic fluid surrounding it to allow for clear imaging. Before 18 weeks, some organs may be too small or underdeveloped to assess accurately, while after 22 weeks, the baby's size can sometimes make it harder to get clear views of all structures due to crowding. This timing balances development and visibility.

How accurate are due dates calculated from the last menstrual period?

Due dates calculated from the last menstrual period (LMP) are generally accurate for individuals with regular 28-day menstrual cycles, with a standard deviation of about 7-10 days. The Naegele's Rule, which adds 280 days (40 weeks) to the LMP, is a common method. However, for those with irregular cycles or unknown LMP, an early ultrasound in the first trimester typically provides a more reliable estimated due date, sometimes shifting the initial LMP-based date by a week or more.

What happens if I miss my anatomy scan window?

If you miss your anatomy scan window, it is crucial to contact your healthcare provider immediately to discuss your options. While the ideal window is 18–22 weeks, scans can sometimes be performed slightly later, though visualization may become more challenging as the baby grows larger and amniotic fluid volume relative to fetal size decreases. Missing the window may limit the ability to detect certain conditions or require additional follow-up scans, so prompt communication with your doctor is essential.