Pregnancy Calculator

Estimate key pregnancy dates and milestones using three clinically-aligned approaches: by Last Menstrual Period (LMP), by Conception Date, or by a known Due Date. This tool helps you map out the due date, gestational age (weeks + days), trimester timing, and common appointment windows—useful when planning prenatal visits, preparing questions for your provider, or comparing estimates to ultrasound dating. You can also explore more tools from All Calculators and browse additional wellness tools in Health & Fitness.

Runs locally in your browser (privacy-first) Uses standard obstetric dating heuristics (estimates) Weeks shown as integer + remaining days

Last Updated: 17 Jan 2026 • This page provides estimates and is not medical advice. For clinical dating, ultrasound and a healthcare professional’s guidance are the reference standard.

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Choose a calculation mode and enter your date.

Calculate pregnancy dates

Tip: ISO date inputs prevent locale confusion

Calculation mode

LMP mode is the most common starting estimate (40 weeks/280 days). Conception mode is useful when you track ovulation. Due-date mode builds a reverse timeline.

LMP date (first day of last menstrual period)

Enter the relevant date for the selected mode. You can set an “as of” date below if you want to calculate for a different day than today.

As of date (optional)

Leave blank to use your device’s local “today.” This is helpful for reviewing past or future milestones.

Average cycle length (days)

Optional. Common range is 21–35. This calculator allows 20–45. For LMP dating, a different cycle length shifts the estimate by (cycleLength − 28) days.

Multiple pregnancy (twins/triplets)

Informational note only

This does not change the formula. It adds a gentle reminder that clinical dating and care plans can differ for multiples.

If checked, results will include an informational disclaimer—your provider may use different monitoring and delivery planning.

Luteal phase length (days)

Optional advanced. Typical range 11–15. If used, ovulation ≈ cycleLength − lutealPhase, and conception estimate ≈ LMP + (cycleLength − lutealPhase).

Quick assumptions

“Luteal-based” affects the estimated conception date and the gestational age conversion for conception mode (still an estimate).

Looking for related health estimators? Many people pair pregnancy planning with tools like a BMI Calculator or a Basal Metabolic Rate Calculator when discussing nutrition goals with a clinician. (Always personalize advice with your healthcare team.)

Premium results view with timeline + breakdown

Your estimated pregnancy timeline

Waiting for input

Estimated Due Date (EDD)

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Calculated from your selected mode and assumptions.

Current Gestational Age (as of selected date)

0 weeks 0 days

Weeks are whole weeks, days are the remainder.

Days until due date

0 days

If negative, you are past the estimated due date (common if dates differ from clinical dating).

Trimester status

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Trimester ranges: 1st (0–13w6d), 2nd (14–27w6d), 3rd (28–40w6d).

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0d of week

0 weeks — 40 weeks

Progress is displayed against a typical 40-week (280-day) timeline.

Step-by-step breakdown

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Rounding policy: gestational age is shown as whole weeks plus remaining days. Dates are shown in a consistent day–month–year format for clarity.

Important: This calculator provides estimates for planning and education. A healthcare professional may date pregnancy differently (often using ultrasound or clinical assessment). If you have concerns about your dates or symptoms, contact a qualified clinician.

Understand what the dates mean

Interpretation guide

Pregnancy dating can feel confusing because gestational age is usually counted from the first day of the last menstrual period (LMP), which is typically about two weeks before conception. That’s why a “40-week pregnancy” is often described as 38 weeks from conception. If your cycles are longer or shorter than 28 days, the estimate may shift—this calculator applies a simple adjustment to reflect that.

EDD is an estimate, not a deadline; babies often arrive within a window.
Gestational age is shown as whole weeks + days remainder, which matches many clinic-style summaries.
Milestones help plan typical windows (e.g., anatomy scan range). Always confirm with your provider.
If you want a due-date-only tool, see our Due Date Calculator.

Prefer quick context? Your copied summaries are plain text and include assumptions (mode, cycle length, and as-of date) so you can share them easily.

Accuracy & Method

What this calculator does (and doesn’t)

All calculations run directly in your browser. Your inputs stay on your device and are not transmitted. This tool uses standard obstetric dating heuristics: 280 days from LMP, 266 days from conception, and a cycle-length adjustment for non-28-day cycles. These are widely used for initial estimates, but clinical dating may differ.

Local-only: privacy-first by design.
Consistent formatting: dates use a clear day–month–year style.
No harsh alerts: warnings are shown gently for unusual inputs.
Not medical advice: consult a clinician for decisions or symptoms.

If you’re also tracking wellness metrics during pregnancy, tools like a Body Fat Calculator can be useful for general education—but always interpret health metrics in pregnancy with professional guidance.

Need a quick check?

Validation reminders

LMP date: can be up to 7 days in the future with a warning; beyond that is likely a typo.
Conception date: can be up to 2 days in the future with a warning; beyond that is likely incorrect.
Due date: unusual ranges (e.g., over 52 weeks away) will show a warning but still compute.
Cycle length: must be 20–45 days; luteal phase: 10–18 days.

If you see a warning, you can still compute (where safe) and then adjust your inputs. This is especially useful when you are comparing estimates from different sources.

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How it works

This Pregnancy Calculator offers three ways to estimate pregnancy timing. Each method starts from a different “anchor” date and then builds the same set of outputs: an estimated due date (EDD), gestational age as of your chosen “as of” date, trimester ranges, and a milestone timeline. The results are designed for planning—such as mapping prenatal visit windows—not for replacing clinical assessment. For related wellness tools, you may also find the Calorie Calculator helpful when discussing nutrition with a professional.

Key dating concepts:

LMP = First day of your last menstrual period (common clinical “start” for gestational age).
Conception date = Approximate day fertilization occurred (often near ovulation, but timing varies).
Cycle length adjustment = A heuristic shift when your average cycle differs from 28 days.
Luteal phase = Days from ovulation to the next period; helps estimate ovulation timing if known.

Formulas used (estimates): The standard obstetric estimate treats pregnancy length as 280 days (40 weeks) from LMP. If you enter a conception date instead, the estimate is 266 days (38 weeks) from conception. If your cycle length differs from 28 days, LMP-based EDD is adjusted by (cycleLength − 28) days, which is a common heuristic used for initial estimates.

Primary calculations:

EDD from LMP: EDD = LMP + 280 days + (cycleLength − 28)
EDD from Conception: EDD = Conception + 266 days
Reverse timeline from Due Date: LMP ≈ DueDate − 280 days (then GA uses that LMP)

Optional advanced estimate:

Ovulation estimate: Ovulation ≈ cycleLength − lutealPhase
Conception estimate from LMP (approx): Conception ≈ LMP + (cycleLength − lutealPhase)

Gestational age (GA): GA = (asOfDate − LMP) in days → weeks = ⌊days/7⌋, daysRemainder = days % 7

Trimester boundaries: 1st trimester runs from 0w0d to 13w6d. 2nd trimester begins at 14w0d and runs to 27w6d. 3rd trimester begins at 28w0d and runs to 40w6d. If your gestational age goes beyond 41w0d by the estimate, the tool labels it as “Post-term” as a timeline description (not a clinical diagnosis).

Milestones timeline: The timeline includes an estimated conception date, trimester transitions, a general anatomy scan window (18w0d–22w6d), a “viability” marker at 24w0d (informational), and a general full-term window (39w0d–40w6d). These are commonly discussed ranges, but your care plan should be personalized.

Practical use cases

People use pregnancy date estimates for many everyday planning tasks. Here are common reasons you might use this Pregnancy Calculator, regardless of whether you start from LMP, conception date, or a known due date.

Prepare for prenatal appointments by knowing your approximate gestational age and trimester.
Plan typical milestone windows (like the 18–22 week anatomy scan range) and compare to a clinic schedule.
Create a simple week-by-week view to track progress and set personal reminders for questions to ask your provider.
Estimate due date timing for practical planning (work arrangements, travel considerations, support planning).
Compare LMP-based and conception-based estimates if you track ovulation or used fertility awareness methods.
Build a reverse timeline when you were given an estimated due date and want to understand the implied LMP and trimester dates.

Worked examples

The examples below show how the calculator turns your inputs into dates. They are worked by hand using the same logic implemented in the tool. Your actual results may differ slightly depending on the “as of” date you choose and whether you apply cycle length or luteal assumptions.

Example 1

Calculate by LMP with standard 28-day cycle

Inputs: LMP = 01 Nov 2025, cycle length = 28, luteal = 14 (not required), as-of date = 17 Jan 2026. Goal: Find EDD and gestational age on 17 Jan 2026.

EDD formula: EDD = LMP + 280 days + (cycleLength − 28)
Substitute values: EDD = 01 Nov 2025 + 280 + (28 − 28) = 01 Nov 2025 + 280 days
Result: EDD is approximately early Aug 2026 (the calculator shows the exact calendar date).
Gestational age: GA days = (17 Jan 2026 − 01 Nov 2025) → convert to weeks + days remainder.
Interpretation: GA is shown as whole weeks plus remaining days, and trimester status follows the 0–13w6d / 14–27w6d / 28–40w6d boundaries.

Example 2

Calculate by Conception date (38-week method)

Inputs: Conception = 15 Dec 2025, as-of date = 17 Jan 2026. Goal: Find EDD and gestational age using conception-based dating.

EDD formula: EDD = Conception + 266 days
Substitute values: EDD = 15 Dec 2025 + 266 days
Gestational age conversion: Clinics often express GA from LMP, roughly 14 days earlier than conception. The calculator estimates an LMP-equivalent date as Conception − 14 days (or uses luteal-based conversion if chosen).
GA calculation: GA days = asOf − estimated LMP-equivalent → weeks + remainder days
Interpretation: This method is useful if you have a well-defined conception estimate (e.g., ovulation tracking), but it remains an estimate because implantation timing can vary.

Example 3

Calculate by Due Date (reverse timeline)

Inputs: Due date = 20 Sep 2026, as-of date = 17 Jan 2026. Goal: Estimate implied LMP and current gestational age on 17 Jan 2026.

Reverse LMP estimate: LMP ≈ DueDate − 280 days
Substitute values: LMP ≈ 20 Sep 2026 − 280 days
Compute GA: GA days = asOf − LMP → weeks + remainder days
Milestones: Once LMP is estimated, all milestones (trimester boundaries, anatomy scan window, etc.) are computed relative to LMP.
Interpretation: This mode helps you visualize where you are in the timeline if you were given a due date but want to understand trimester ranges and milestone timing.

Note: For a dedicated due-date estimator without timelines, you can also use the Due Date Calculator. This page focuses on a broader pregnancy timeline view.

Common mistakes to avoid

Pregnancy dating is sensitive to small input differences. A single day change can shift milestone windows, and cycle length differences can shift the estimate further. Here are frequent issues that lead to confusing results.

Entering the last day of bleeding instead of the first day of the last menstrual period for LMP mode.
Mixing up conception date with ovulation day or implantation day (they can differ).
Forgetting cycle length adjustment when cycles are consistently longer/shorter than 28 days.
Using an “as of” date far in the future by mistake (or leaving it set when you meant “today”).
Assuming the EDD is a fixed deadline rather than a planning estimate.
Using luteal phase values that are outside typical ranges or not stable from cycle to cycle.

Quick tips for better estimates

These tips help you get a clearer timeline and make your copied summary more useful when sharing with a clinician, partner, or planning document.

If you’re unsure of the exact LMP day, use your best estimate and treat the result as approximate.
Use the as of date when you want to check milestones for a future appointment date.
If your cycles are consistently 32 days, keep cycle length at 32 to see the typical adjustment (+4 days).
If you track ovulation and know your luteal phase is stable, enabling luteal assumptions can refine the conception estimate.
Copy “Full Summary” before appointments so assumptions (mode + cycle length) are preserved in plain text.
Compare the calculator’s estimated conception date with your tracking—differences can be a helpful discussion point.

Sources & References

The calculation methods reflect common, standard obstetric dating concepts used for initial pregnancy estimates. For patient-facing explanations, many clinicians reference guidance from professional organizations (for example, ACOG patient education) and standard gestational age conventions (LMP-based dating, trimester boundaries, and typical scan windows). This page does not link out and is provided for general informational use.

Standard dating convention: 280 days from LMP (40 weeks)
Conception-based convention: 266 days from conception (38 weeks)
Trimester boundaries: 0–13w6d, 14–27w6d, 28–40w6d
Milestone windows: anatomy scan timing and full-term guidance ranges (general)

FAQ

These answers explain what the Pregnancy Calculator shows and how to interpret the estimates. The goal is clarity: what the dates mean, why methods differ, and how to use the timeline responsibly.

Which date should I use: LMP, conception, or due date?

Use the date you’re most confident about. LMP is the most commonly used starting point for early estimates because it’s easier to identify for many people, even though it’s usually about two weeks before conception. Conception date can be helpful if you track ovulation closely or have a known fertilization window, but it can still be approximate. Due-date mode is useful when a clinic gave you an estimated due date and you want the implied LMP, trimester ranges, and milestones for planning.

Why does a “40-week pregnancy” not equal 40 weeks from conception?

Gestational age is typically counted from the first day of the last menstrual period (LMP), not from the day of conception. In a typical cycle, ovulation and conception occur roughly two weeks after LMP, so “40 weeks pregnant” by gestational age is often about 38 weeks after conception. This convention helps standardize dating when conception isn’t known. If your cycles are longer or shorter than 28 days, the timing of ovulation may shift, and the calculator’s cycle-length adjustment provides a practical estimate.

How does cycle length change my estimated due date?

Many quick estimates assume a 28-day cycle. If your average cycle is longer, ovulation tends to occur later, and an LMP-based due date may shift later as well. This calculator applies a common heuristic: EDD = LMP + 280 days + (cycleLength − 28). For example, if your cycle length is 32 days, the estimate shifts by +4 days. If your cycle length is 24 days, it shifts by −4 days. This is still an estimate and may differ from clinical dating.

What does luteal phase mean, and should I change it?

The luteal phase is the time between ovulation and the next period. Many people have a luteal phase around 12–14 days, but it can vary. In advanced mode, luteal phase helps estimate ovulation timing using ovulation ≈ cycleLength − lutealPhase. If you know your luteal phase is consistently, for example, 12 days, the estimated conception date from LMP can be refined. If you don’t track it confidently, leaving the default (14) is usually best, because changing it without reliable information can introduce extra error.

What is the anatomy scan window shown in the timeline?

The calculator shows a general anatomy scan window of 18w0d to 22w6d. This is a common range discussed for the mid-pregnancy ultrasound that reviews fetal anatomy and growth. Exact scheduling varies by region, clinic workflow, and individual circumstances, so treat it as a planning window rather than a guaranteed appointment date. If you’re booking ahead, using the “as of” date can help you see whether you’ll be within that window on a specific day and plan questions for your provider.

What does “viability milestone (24 weeks)” mean here?

The “viability milestone” at 24w0d is labeled as informational because viability depends on many factors, including gestational age accuracy, clinical resources, and individual health considerations. The timeline marker is included because 24 weeks is often referenced in general education materials, but it should not be used for medical decision-making. If you have concerns about pregnancy progression, symptoms, or dating accuracy, the safest next step is to consult a qualified clinician who can interpret your situation in context.

Why might my ultrasound due date differ from this calculator?

Ultrasound dating can differ because it measures fetal size and growth patterns that may provide a more individualized estimate, especially early in pregnancy. LMP-based estimates assume typical ovulation timing and a stable cycle, but real cycles vary. Conception timing can also be uncertain if ovulation and implantation weren’t tracked. This calculator’s purpose is to provide a consistent planning timeline; if you have an ultrasound-based due date from a clinician, it’s often the better anchor for medical care. Due-date mode can help you visualize that timeline.

Is it normal to go past the estimated due date?

Yes. An estimated due date is not a guaranteed delivery date; it’s a midpoint estimate. Many births occur before or after it, and the “days until due date” counter can become negative if your as-of date is later than the estimate. The calculator also shows a general full-term window of 39w0d–40w6d as a planning range. If you are approaching or past your due date, clinical monitoring and decisions should be guided by your healthcare professional, who will consider your specific situation.

Does selecting “multiple pregnancy” change the due date calculation?

No. The toggle is informational only and does not change the EDD formula. While multiples can affect monitoring schedules and delivery planning, changing the due date formula without clinical context can be misleading. The calculator keeps a consistent method and adds a gentle reminder that twins or higher-order multiples may follow different care pathways. If you are carrying multiples, your provider is the best source for interpreting dates, monitoring frequency, and timing decisions, especially if you have ultrasound-based dating information.

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