How to Use the Pregnancy Week Calculator

If you’ve ever typed “what week of pregnancy am I” or “how many weeks pregnant am I” into a search bar, you already know the answer isn’t always obvious. Pregnancy is measured in a slightly unusual way — weeks are counted from before conception even happens — and different people have different pieces of information on hand: a period date, a due date from a provider, or a known conception date. This guide walks through how the Pregnancy Week Calculator works, how to add it to a WordPress page, and how to read and make sense of the results it gives you.

What the calculator does

At its core, the tool answers one question in three different ways: given the information you have, how many weeks and days pregnant are you right now (or on any date you choose)?

It supports three common starting points:

• Last menstrual period (LMP) — the first day of your most recent period. This is the standard reference point used in obstetrics for dating a pregnancy, even though conception itself happens roughly two weeks later.
• Estimated due date — if a provider or an earlier calculator has already given you a due date, you can work backward from that.
• Conception date — useful if you know it precisely, for example from fertility tracking or an assisted conception. This is one of the less commonly used inputs but is included for completeness.

Whichever starting point you use, the calculator converts it to an equivalent LMP date behind the scenes, then measures forward from there using the standard 280-day (40-week) pregnancy convention. That’s why, no matter which tab you use, you should get consistent, comparable results.

Adding it to your WordPress page

1. Open the page or post where the calculator should live, using the WordPress block editor.
2. Insert a Custom HTML block. Click the + icon to add a new block, search for “Custom HTML,” and select it.
3. Paste the entire code block you were given, starting from <div class="pwc-root"> through to the final closing </div>. Don’t split it across multiple blocks — the <style> and <script> sections need to stay attached to the markup they belong to.
4. Preview before publishing. Use the block’s Preview tab or the page preview to confirm the calculator renders and responds correctly.
5. Publish the page. No plugins, shortcodes, or extra configuration are required — everything needed is self-contained in the block.

If you’re using a page builder like Elementor, Divi, Beaver Builder, or similar instead of the native block editor, look for an element called “HTML,” “Code,” “Embed,” or “Custom Code,” and paste the block there instead of into a Custom HTML block.

Common setup issues

• The calculator doesn’t appear at all. This almost always means part of the code got cut off during copy-paste. Make sure the very first line (<div class="pwc-root">) and the very last line (the matching closing </div>) are both present, along with the <script> block in between.
• The layout looks squeezed on desktop. The calculator is designed to sit inside a content column and caps itself at a maximum width, centering automatically. If your theme’s content area is unusually narrow, some elements will simply stack vertically — this is expected, responsive behavior.
• Date inputs look different across browsers. Date fields are rendered using each browser’s native date picker, so the exact look (a calendar pop-up, a text field, three separate dropdowns) will vary slightly between, say, Chrome and Safari, or desktop and mobile. This doesn’t affect accuracy — it’s purely cosmetic and outside the calculator’s control.

How to use it, step by step

1. Choose your dating method. At the top of the calculator, three tabs let you pick which date you’re entering: Last Period, Due Date, or Conception Date. Pick whichever one matches the information you actually have — you don’t need to fill in all three.

2. Enter the date. Click into the date field and select the relevant date. The label above the field and the small hint text beneath it update automatically depending on which tab is selected, so you always know exactly what date you’re being asked for.

3. (Optional) Change “Calculate as of.” By default, the second field is set to today’s date, and the calculator shows how far along the pregnancy is right now. If you want to know how many weeks pregnant someone was on a past date, or will be on a future date — for example, to plan around a trip, a work deadline, or a family event — change this field to whatever date you’re curious about. Everything else recalculates instantly.

4. Read the headline result. The large number at the top of the results section is the core answer: weeks and days along, as of the date you chose. Just underneath it, a short sentence spells this out in plain language, and if you changed the “calculate as of” date away from today, it will say so explicitly, so there’s no ambiguity about which date the result refers to.

5. Check the trimester progress bar. Below the headline number, a three-segment bar represents the three trimesters, with a marker showing exactly where the selected date falls. This is a quick visual way to see not just the week number, but roughly how far through the whole pregnancy that week sits.

6. Review the stat cards. Four small cards summarize the most commonly asked-about figures:

• Trimester — which of the three trimesters the date falls into
• Estimated due date — calculated from whichever method was used
• Pregnancy progress — expressed as a percentage of the full 40 weeks
• Days until (or past) the due date — a running countdown, or count-up if the due date has already passed

7. Notice the size comparison. For weeks roughly 4 through 42, the calculator shows a common size comparison (for example, “about the size of a lime” or “about the size of a pineapple”). These comparisons are approximate, vary from source to source, and are included mainly as a friendly, familiar touch rather than a precise measurement.

8. Watch for the warning message. If the dates entered don’t add up — for instance, a last-period date that’s after the “calculate as of” date, or a combination of dates that implies a pregnancy far longer than 40 weeks — a small amber warning box appears explaining the issue. This is a prompt to double-check what was typed in, not an error you need to troubleshoot technically.

Making sense of the numbers

A few things are worth keeping in mind while reading the results:

• Weeks are counted from the last period, not from conception, even on the “Conception Date” tab. This can feel counterintuitive — a pregnancy is often already considered about two weeks along on the day conception actually occurs — but it’s the standard convention used throughout obstetric care, which is why the calculator follows it too, regardless of which input method is used.
• The due date is an estimate, not a prediction. Only a small percentage of pregnancies deliver on the exact calculated due date. The 40-week figure is a useful planning anchor, not a guarantee.
• Trimester boundaries are approximate and vary slightly by source. This calculator uses weeks 1–13 for the first trimester, 14–27 for the second, and 28 and beyond for the third, which is one of the most commonly used conventions, though you may see slightly different week cutoffs elsewhere.
• If you know your due date from an ultrasound, that’s usually the most accurate starting point to use, since early ultrasound dating tends to be more precise than last-period dating alone — particularly for anyone with irregular cycles.

Suggested surrounding content for the page

Since the calculator’s own on-page text updates dynamically based on user input, it won’t carry static keyword phrasing that search engines can index directly. If your goal is to rank for phrases like “pregnancy week calculator,” “what week of pregnancy am I,” or “pregnancy weeks calculator,” it helps to wrap the embed in a page that includes:

• A short introductory paragraph above the calculator using those phrases naturally
• A brief explanation of the three dating methods (similar to the “What the calculator does” section above)
• An FAQ section addressing common follow-up questions, such as how due dates are calculated, why trimester lengths differ slightly between sources, or how accurate the size comparisons are
• Links to any related calculators on your site — a Gestational Age Calculator or Pregnancy Trimester Calculator, for example — since visitors researching one of these tools are often looking for the others too

A note on accuracy and scope

This tool performs a standard date calculation based on the 280-day gestation convention; it doesn’t access any personal health records, doesn’t store the dates entered anywhere, and doesn’t make any assessment of pregnancy health or risk. It’s meant to give a quick, easy-to-understand answer to “what week am I in,” not to replace the dating and monitoring a healthcare provider carries out during actual prenatal care. It’s worth keeping a short disclaimer to that effect visible on the page — the calculator already includes one in its footer, and it’s a good idea to leave that text in place when embedding it.