Four Weeks Pregnant- When Am I Due? | Due Date Math Made Clear

Reaching the four-week mark often brings a mix of excitement and questions. One of the first is about timing. Knowing when your baby may arrive helps with planning appointments, work leave, and personal milestones. The answer depends on how pregnancy weeks are counted and what counts as “week one.” This article breaks that down in plain terms, with clear steps and realistic ranges.

Right away, it helps to know that pregnancy dating does not start at conception. The medical calendar begins earlier, which can feel confusing. Once you see the logic, the math becomes easy to follow.

How Pregnancy Weeks Are Counted

Clinicians date pregnancy from the first day of your last menstrual period, often shortened to LMP. That date becomes day one, even though ovulation and fertilization happen later.

Why this system? The LMP date is easier to identify than the moment of conception. Most cycles follow a steady pattern, so this method gives a shared baseline across clinics and studies.

By this count, ovulation often happens around week two. Implantation tends to occur near the end of week three. By week four, a pregnancy test often turns positive.

What “Four Weeks Pregnant” Means On The Calendar

At four weeks pregnant, it has usually been about two weeks since conception. Hormone levels are rising, and the embryo is beginning early development. Many people feel no symptoms yet, while others notice mild cramping or fatigue.

From a dating view, four weeks means you are 28 days from the first day of your last period. That date anchors your due date calculation.

Calculating Your Due Date From Four Weeks Pregnant

A standard pregnancy lasts 40 weeks from the LMP date. If you are four weeks along, subtract those four weeks from the full term length.

That leaves 36 weeks remaining.

Another way to picture it: add 36 weeks to today’s date. The result gives a working due date. Many clinics still use this approach at early visits.

The Common Formula Doctors Use

One long-standing method is called Naegele’s rule. It follows three steps:

• Start with the first day of your last menstrual period.
• Add one year.
• Subtract three months, then add seven days.

This produces a due date close to the 40-week mark. Clinics now rely on software and ultrasound data, yet the rule explains the logic behind the estimate.

Why Your Due Date Is An Estimate

Only a small share of babies arrive on the exact due date. Most are born within a two-week window before or after it. Cycle length, ovulation timing, and genetics all shape when labor starts.

This is normal. The date acts as a planning guide rather than a fixed appointment.

Four Weeks Pregnant Due Date Range Explained

To put timing into context, here is how a four-week pregnancy usually lines up with delivery timing. This table shows ranges rather than a single day.

Week Marker	What It Means	Timing From Now
Week 4	Early confirmed pregnancy	Today
Week 8	First prenatal visit for many	About 32 weeks left
Week 12	End of first trimester	About 28 weeks left
Week 20	Anatomy scan window	About 20 weeks left
Week 37	Early term begins	About 3 weeks left
Week 40	Estimated due date	About 36 weeks left from week 4
Week 41	Post-term monitoring may start	About 37 weeks left from week 4

What Can Shift A Due Date After Week Four

The first estimate often comes from the LMP date alone. Later checks can fine-tune it. Some changes are small, while others adjust the date by several days.

Ultrasound Dating

An early ultrasound, often done between weeks seven and ten, measures the embryo’s length. This measurement can adjust the due date if it differs from the LMP estimate by several days.

Many providers treat this scan as the most reliable dating tool. Guidance from the American College of Obstetricians and Gynecologists explains how early measurements guide this decision.

Cycle Length Differences

Not everyone has a 28-day cycle. Longer or shorter cycles shift ovulation timing. If your cycles tend to be longer, ovulation may have happened later, nudging the due date back.

Sharing cycle history at your first visit helps clinicians interpret early data.

Assisted Reproduction Timing

With treatments like IVF, the exact fertilization date is known. Clinics calculate due dates from embryo transfer timing rather than the LMP date. This can change the calendar by several days.

How Four Weeks Pregnant Fits Into Trimesters

Pregnancy is often grouped into three trimesters. Knowing where week four sits helps frame what comes next.

• First trimester: Weeks 1 through 12.
• Second trimester: Weeks 13 through 27.
• Third trimester: Weeks 28 through 40.

Week four sits near the start of the first trimester. Many changes happen behind the scenes, even if outward signs are subtle.

The NHS week-by-week pregnancy overview outlines what is happening at this stage and what care usually begins soon after.

Four Weeks Pregnant- When Am I Due Based On Common Scenarios

This section answers the question in practical terms by walking through real-world situations that often come up.

If You Know Your Last Period Date

Take the first day of that period. Add 40 weeks. If you are four weeks pregnant today, count 36 weeks ahead to find your estimated delivery date.

If Your Periods Are Irregular

The first estimate still uses the LMP date. An early ultrasound often refines it. Many people with irregular cycles see small adjustments after that scan.

If You Tested Positive This Week

A positive test at week four lines up with rising hCG levels. The due date math stays the same, based on LMP, until ultrasound data is available.

Why Doctors Talk About A Due Window, Not One Day

Labor starts when hormonal and physical signals align. That timing varies from person to person. Research summarized by the Mayo Clinic shows most births cluster in the two weeks around the due date.

This window guides monitoring and planning. It also helps reduce stress when the calendar day passes without labor starting.

Planning Ahead From Week Four

Once you have a working due date, even an early one, you can map out the next steps. This helps with scheduling and personal planning.

Medical Milestones

Many clinics schedule the first prenatal visit between weeks eight and ten. Screening options, lab work, and ultrasound timing flow from the due date estimate.

The Centers for Disease Control and Prevention pregnancy guidance outlines early care steps and timelines.

Work And Personal Planning

A due date helps estimate maternity or parental leave timing, childcare planning, and travel cutoffs. Treat the date as a planning anchor rather than a deadline.

Quick Reference: Four Weeks Pregnant Timing At A Glance

Detail	Timing	Notes
Current gestational age	4 weeks	Counted from LMP
Weeks remaining	36 weeks	Based on a 40-week term
Likely delivery window	Weeks 38–42	Most births occur here
First prenatal visit	Weeks 8–10	Varies by provider
First trimester end	Week 12	Early screenings often complete

Common Questions That Come Up At Week Four

Many people ask if their due date will change later. Small shifts happen, often after the first ultrasound. Larger changes are less common once early dating is set.

Others ask whether conception date matters more than the period date. In routine care, the period date anchors the calendar, with ultrasound data refining it.

These points help set expectations early and reduce confusion later on.