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Pregnancy Calculator | Track Pregnancy Week, Due Date, Milestones

Estimate your due date from the last menstrual period or conception date, and track your current week, trimester and key milestones. The standard 40-week rule applied with clear dates — a planning companion for expecting parents (confirm with your provider).

Last updated: June 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Pregnancy stage	Typical weeks
First trimester	Weeks 1–12
Second trimester	Weeks 13–27
Third trimester	Weeks 28–40
Full term	About 39–40 weeks

monitor_weight A starting point, not a diagnosis

This calculator gives you the same number a clinician would compute by hand from your inputs. It is informational, never a substitute for a doctor. If a result surprises you, write it down and discuss it at your next appointment — that conversation is the goal, not a verdict from a webpage.

science Built from peer-reviewed formulas

Every health calculator on CalcaTools uses an equation from the WHO, NIH, ACOG, CDC, or a published peer-reviewed paper. The exact citation is in the "Formula & methodology" section. We re-check sources quarterly and update the page when guidance changes — the "Last reviewed" date is at the top.

volunteer_activism Designed for real people

Health calculations only help if you can actually use them. We use plain-English labels (no jargon), accept both metric and US units, and show what a "normal" range looks like alongside your result — so you understand what the number means, not just what it is.

lock Private by design

Your weight, height, age, pregnancy details, and any other health input never leave your browser. Calculations run client-side; nothing is logged or stored on our side. We don't want your medical data — we just want the formula to work for you.

Interpretation guide

Input	Use it for
Last menstrual period	Standard Naegele rule estimate
Conception/ovulation date	Useful when known accurately
Ultrasound dating	Clinician-confirmed dating may override calculator estimates

lightbulb Worked example

Let's say you are using the Pregnancy Calculator. Tracks a pregnancy from the last menstrual period or conception date. Enter your LMP or conception date, and the tool calculates your current pregnancy week and day, the trimester, the estimated due Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula Estimated due date = LMP + 280 days and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: Estimated due date = LMP + 280 days

The Pregnancy Calculator is built on a well-established calculation method. It uses the formula Estimated due date = LMP + 280 days to turn your inputs into a reliable result. Tracks a pregnancy from the last menstrual period or conception date. Enter your LMP or conception date, and the tool calculates your current pregnancy week and day, the trimester, the estimated due date, and when key The steps are shown on the page so you can follow the reasoning from input to output.

Naegele's rule adds 280 days (40 weeks) to the first day of the last menstrual period. Actual delivery dates vary; only a healthcare professional can provide individualized pregnancy guidance.

Authoritative source: ACOG

Frequently asked questions

How do I use the pregnancy due date calculator?

Enter the first day of your last menstrual period or a conception date, and the tool applies the standard rule Estimated due date = LMP + 280 days (40 weeks), or LMP + 266 days for conception. It then shows your current week of pregnancy, trimester, and key milestone dates. Only about 4% of babies arrive exactly on the due date — it is a 40-week estimate, not a deadline.

What formula does the pregnancy due date calculator use?

The Pregnancy Calculator uses the standard Estimated due date = LMP + 280 days. You enter your values, and the calculator applies the formula step by step, showing the working so you can verify the math and understand how the result is derived rather than trusting a black box.

Is the pregnancy due date calculator accurate?

The Pregnancy Calculator applies the standard formula: Estimated due date = LMP + 280 days. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

Why do my results differ from another calculator?

The Pregnancy Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Tracks a pregnancy from the last menstrual period or conception date. Enter your LMP or conception date, and the tool calculates your current pregnancy week and day, the trimester, the estimated due date, and when key milestones — such as the first and second There is no limit on usage, and it works on any device.

Can the pregnancy due date calculator replace professional advice?

No — it estimates the due date with the standard LMP + 280 days rule and tracks weeks, but it is not a medical tool: it does not account for ultrasound findings, cycle irregularities, multiple pregnancies, or health conditions that change dating. Always confirm your due date with a healthcare provider, ideally from an early ultrasound, and follow their schedule for care.

What does the Pregnancy Calculator do?

Tracks a pregnancy from the last menstrual period or conception date. Enter your LMP or conception date, and the tool calculates your current pregnancy week and day, the trimester, the estimated due date, and when key milestones — such as the first and second. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.

What formula does the Pregnancy Calculator use?

It applies the standard rule: estimated due date = first day of the last menstrual period + 280 days (40 weeks), or LMP + 266 days from the conception date if you enter that instead. The current pregnancy week is then computed from the difference between today and the LMP. This is the same Naegele's rule obstetricians use before ultrasound dating.

Is the Pregnancy Calculator free and private?

Yes — the Pregnancy Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.

How accurate is the Pregnancy Calculator?

The LMP-based due date is accurate for regular 28-day cycles but can be off by a week or more for irregular cycles or unknown LMP. Early ultrasound dating (8–12 weeks) is the most accurate method, accurate to about ±5 days. Only about 4% of babies arrive on the due date exactly — the date is a 40-week midpoint, and full-term delivery spans 37–42 weeks.

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