Pregnancy Week Calculator: Track Your Week-by-Week Progress

How to Use Pregnancy Week Calculator: Track Your Week-by-Week Progress

1. Step 1: Choose a dating method

   Pick LMP (last menstrual period), Due Date, Conception date, or Ultrasound. The calculator adjusts formulas automatically.

2. Step 2: Enter the required date(s)

   Provide the date for your chosen method. For Ultrasound, enter the scan date and the measured weeks + days.

3. Step 3: See your current week

   Your gestational age shows as weeks + days with the current pregnancy week highlighted.

4. Step 4: Review EDD and milestones

   Check the estimated due date, trimester, and the timeline of upcoming weeks for planning.

5. Step 5: Save or share your summary

   Copy the summary to notes or share with a partner. Revisit anytime—no sign‑in and no data storage.

Key Features

• Current week and days
• Estimated due date (EDD)
• Trimester and key milestones
• Flexible methods: LMP, due date, conception, ultrasound
• Week‑by‑week table

Understanding Results

How the Pregnancy Week Calculator Works (Formula)

Gestational age (GA) counts from the first day of the last menstrual period (LMP). By convention, pregnancy is 40 weeks (280 days) from LMP or 38 weeks (266 days) from conception. The calculator supports four common methods and converts them into the same GA scale so your week number is consistent.

LMP method: GA = Today − LMP. Due date (EDD) = LMP + 280 days. Due‑date method: GA = 280 − (EDD − Today). Conception method: GA = (Today − Conception) + 14; EDD = Conception + 266. Ultrasound method: use the scan date and measured GA to anchor the timeline; EDD = Scan date + (280 − measured GA in days).

Reference Ranges & Interpretation

Most single‑pregnancy timelines span 37–42 completed weeks. Trimester boundaries are commonly defined as: First (0–12w6d), Second (13–27w6d), Third (28w0d to birth). Anatomy scans are often scheduled around 18–22 weeks, and term is usually considered from 37 weeks. Schedules may vary by clinician and clinical context.

Assumptions & Limitations

Dates are estimates for planning and education—not medical advice. Early ultrasound dating is generally more precise than calendar methods. Cycle irregularity, late ovulation, IVF protocols, or uncertain dates can shift the actual GA. If anything looks off or you have symptoms or concerns, contact your clinician.

Complete Guide: Pregnancy Week Calculator: Track Your Week-by-Week Progress

Use the pregnancy week calculator to see your current week and days, trimester, and estimated due date. Choose LMP, due date, conception, or ultrasound dating.

What this calculator shows

This pregnancy week calculator is built for clarity. It answers the most practical questions in seconds: What week am I in? How many weeks and days pregnant am I today? When is my estimated due date (EDD)? Which trimester am I in, and what’s coming up next? The tool is flexible—you can start from LMP, a provided due date, a known conception date, or the gestational age from an ultrasound report. Whichever you pick, the result is displayed on the same consistent gestational‑age scale used by clinicians.

The result card shows your completed weeks and extra days, a week label (Week 1, Week 2, …), your trimester, and the next major milestone. A compact week‑by‑week table gives you a short‑term view of the coming weeks with actual calendar dates. Nothing is stored or sent anywhere—everything runs privately in your browser.

Ways to date a pregnancy

LMP (last menstrual period): The most familiar starting point. If you know the first day of your last period, the calculator treats that as day 0. By convention, a full‑term pregnancy is 40 weeks (280 days) from LMP. This approach is straightforward but assumes ovulation occurred roughly two weeks later, which is not always the case for irregular cycles.

Due date (EDD): If your clinician has already provided a due date, you can enter it directly. The calculator works backward to show your current gestational age and a derived LMP for your timeline. This is useful when your care team has reconciled LMP and ultrasound information and finalized an EDD.

Conception/ovulation/transfer date: If you track ovulation closely, used an ovulation predictor kit, underwent IUI/IVF, or know the embryo transfer date, you have a more precise anchor for conception. Clinically, gestational age runs about two weeks ahead of conception age, so the calculator adds 14 days to map your result to the standard GA scale. EDD is then conception + 266 days (38 weeks).

Ultrasound: Early pregnancy ultrasounds estimate gestational age based on biometric measurements, such as crown‑rump length. If your report says, for example, “8 weeks 3 days on April 4,” the calculator uses that as a solid anchor and projects forward and backward. Early scans are generally more precise than calendar‑only methods.

How gestational age is calculated

Clinicians speak in gestational age, not embryonic age. Gestational age starts on day 1 of the cycle (LMP). Many people ovulate about two weeks later, so gestational age runs about two weeks ahead of the embryo’s actual age. That is why you can be “4 weeks pregnant” before a positive test or long before a first prenatal visit. It is a standardized way to talk about pregnancy timing and to schedule tests and visits.

Mathematically, these are the conversions the tool uses: LMP method → GA = Today − LMP; EDD method → GA = 280 − (EDD − Today); Conception method → GA = (Today − Conception) + 14; Ultrasound method → once we know the scan date and measured GA in days, GA(today) = GA(scan) + (Today − Scan date). All methods end up on the same timeline so your week label is consistent regardless of how you started.

When you are told you are in “week 13,” it usually means you have completed 12 full weeks and are currently in the 13th week. The calculator shows both formats: completed weeks + days and a week label so you can speak either way.

Trimester boundaries and milestones

Trimesters are convenient segments of the 40‑week timeline. A common convention is: First trimester from LMP to 12 weeks + 6 days, Second trimester from 13 weeks to 27 weeks + 6 days, and Third trimester from 28 weeks onward. Clinics may adjust certain scheduling details, but these ranges are widely used for planning.

Your care team may schedule specific visits or screenings at approximate windows along this arc. For example, a comprehensive anatomy scan is often scheduled around 18–22 weeks. Policies vary by region and clinical setting, so always follow your clinician’s guidance. The calculator’s timeline simply helps you visualize what the next several weeks look like on the calendar and how they relate to commonly referenced milestones.

If you started the calculator from an ultrasound, your gestational age line originates from measured growth rather than a calendar assumption. Early ultrasound dating is typically more precise than LMP alone. Organizations like ACOG recommend using earliest reliable dating to set or confirm the EDD so everyone refers to the same schedule thereafter.

Common scenarios and examples

Regular cycles, confident LMP: You know the first day of your last period, your cycles are typically predictable, and you are early in pregnancy. LMP is a fine place to start. The calculator will show a due date by adding 280 days and a week table for the next several weeks.

Irregular cycles or unknown LMP: If you are less confident about your last period date, start from an ultrasound report if you have one. Otherwise, use a provided due date. If neither is available yet, you can estimate by conception or ovulation if you tracked it closely using kits or basal body temperature. For planning ovulation, our Ovulation Calculator may help for the next cycle.

Known conception or IVF: If you conceived via IUI/IVF or know your ovulation/trigger timing, the conception method provides a strong anchor. The tool adds 14 days to map to gestational age and projects an EDD 266 days from conception. If you had an embryo transfer, use the transfer date. For broader planning around luteal timing, see our Luteal Phase Calculator.

EDD provided by your care team: Enter the due date as is. The calculator will show today’s gestational age and a derived LMP date for a consistent week table. This approach is useful after your clinician reconciles LMP and ultrasound dates and confirms a final EDD.

Planning around tests: Many people like to know when a home pregnancy test is likely to turn positive. If you are still before a missed period, our Pregnancy Test Calculator suggests earliest and recommended testing windows based on ovulation timing. If you are tracking cycles, Next Period Calculator can also help you anticipate the right time to test.

Ultrasound dating vs. LMP

An early ultrasound anchors gestational age to observed growth. When ultrasound dating and LMP disagree meaningfully, clinicians often prefer early ultrasound because it reduces error introduced by cycle variability. If your EDD is adjusted based on a scan, the calculator’s due‑date method will reflect the updated schedule immediately.

Professional bodies such as the American College of Obstetricians and Gynecologists (ACOG) summarize dating recommendations and the windows where ultrasound is most informative for establishing a due date. If you want to read further, see ACOG’s committee opinion on methods for estimating due date (external). ACOG guidance.

What affects accuracy

No calculator can confirm ovulation day or embryonic age on its own. Cycle irregularity, delayed ovulation, variability in implantation, and differences in fetal growth all introduce uncertainty. Early ultrasound typically narrows this uncertainty. As pregnancy progresses, your care team may refine plans based on clinical findings and context.

Twins and higher‑order multiples can also change timelines. Clinical management of multiple gestations differs from singletons, including how and when certain scans and visits are scheduled. Always rely on your clinician’s recommendations if you are carrying multiples or have any medical considerations.

Because GA is a standardized planning tool rather than a measurement of exact fetal age, focus on using the timeline to coordinate visits, tests, and personal logistics, not to judge day‑to‑day progress. The calendar is there to help you prepare and communicate clearly with your care team.

Using your results

Use the current week label and your EDD as a shared reference with partners, family, and your clinician. The week‑by‑week table shows upcoming week boundaries with real dates so you can plan appointments, travel, and support. If your dates change based on a scan, simply switch methods to Due Date or Ultrasound and your timeline updates instantly.

For broader pregnancy planning (tests, ovulation timing, and due date estimation), try these related tools: the Pregnancy Due Date Calculator, the all‑in‑one planning view in the Pregnancy Calculator (All‑in‑One), and the Ovulation Calculator if you are still in the conception phase.

If you are looking up general background, authoritative public‑health sources are a good starting point. The U.S. Centers for Disease Control and Prevention (CDC) provides accessible pregnancy basics and timelines. CDC pregnancy resources.

Related tools and next steps

• Pregnancy Due Date Calculator — confirm or compare your EDD using LMP, conception, or ultrasound inputs.
• Pregnancy Calculator (All‑in‑One) — a consolidated view of key dates and planning helpers.
• Ovulation Calculator — plan conception with a fertile‑window timeline.
• Luteal Phase Calculator — understand timing between ovulation and the next period.
• Pregnancy Test Calculator — earliest vs. best date to test based on ovulation timing.

This guide is informational and cannot replace personalized medical advice. If you have questions about symptoms, timing, or results, contact your clinician. Use your calculated week as a helpful conversation starter and planning aid.

Frequently Asked Questions