Due Date Calculator

A due date is an estimated time when a pregnancy reaches about 40 weeks of gestational age. This calculator helps you estimate an expected due date using common clinical dating methods (Last Menstrual Period, conception date, or IVF/embryo transfer) and then shows your current pregnancy progress as of your local “today” date—useful for planning appointments, timelines, and milestones. If you’re comparing dates across tools, our Date Calculator can help you verify day counts, and you can explore more tools in All Calculators.

Calculate your estimated due date

Choose the method that best matches the information you have. Each method uses standard day-level dating assumptions.

Uses the first day of your last menstrual period (LMP) and adjusts the standard 40-week estimate by your cycle length compared with a 28-day baseline.

Typical range is 20–45 days. We’ll show a gentle note if it’s unusual.

If you know the conception date (for example, a confirmed ovulation date), we estimate a due date at 38 weeks from conception and derive gestational age using a standard 14-day offset.

For IVF, select your embryo transfer date and embryo age (Day 3/5/6). We estimate a due date using standard IVF dating and compute gestational age from an LMP-equivalent reference.

Choose the embryo age reported by your clinic.
Enter your details above, then calculate.

How it works (formulas & definitions)

Due date estimates are based on standardized “gestational age” dating. In obstetrics, gestational age is counted from the first day of the last menstrual period (LMP), even though conception typically occurs about two weeks later. When you use a conception date or IVF transfer date, we convert those details into an LMP-equivalent reference point so pregnancy weeks and trimesters can be displayed consistently.

Core methods used

  • LMP method: AdjustmentDays = CycleLength − 28, then DueDate = LMP + 280 + AdjustmentDays. This follows the standard 40-week framework with a cycle-length adjustment.
  • Conception date method: DueDate = ConceptionDate + 266 days (38 weeks). For gestational age, we assume LMP_equivalent = ConceptionDate − 14 days.
  • IVF / embryo transfer method: Let EmbryoAgeDays ∈ {3,5,6}. Then DueDate = TransferDate + (267 − EmbryoAgeDays) days. We compute an LMP-equivalent baseline as LMP_equivalent = TransferDate − (EmbryoAgeDays + 14) days.

Precision & rounding: dates are normalized to your local midnight to avoid off-by-one issues, and displayed at day-level granularity. Pregnancy weeks are shown as whole weeks plus remaining days.

When results can differ: ovulation timing can vary, cycles can be irregular, and clinicians may update dating based on early ultrasound measurements or IVF records. Use this calculator for planning—not diagnosis.

Use cases

Planning prenatal appointments

Estimate timing for early visits, screening windows, and a likely anatomy scan range so you can schedule ahead.

Work & leave preparation

Get a realistic due date window to help coordinate parental leave, workload handoffs, and travel decisions.

Tracking IVF timelines

Translate embryo transfer details into a due date and gestational age format commonly used in pregnancy care.

Comparing estimates

See how LMP and conception-based estimates differ when cycle length or ovulation timing is unusual.

Milestone awareness

Understand trimester boundaries, the approximate viability timeframe, and the full-term window for planning.

Worked examples

Example 1: LMP with a 30-day cycle

Inputs: LMP = March 4, 2026; Cycle length = 30 days.

Computation outline: AdjustmentDays = 30 − 28 = 2. Add 280 + 2 = 282 days to the LMP date.

Result summary: Estimated due date is the LMP date plus 282 days. Gestational age today is based on the number of days since LMP, converted into weeks and days.

Example 2: Conception date confirmed

Inputs: Conception date = May 12, 2026.

Computation outline: DueDate = May 12, 2026 + 266 days. For gestational age, compute LMP_equivalent = May 12, 2026 − 14 days, then count days from that date to today.

Result summary: The due date is 38 weeks after conception. The trimester is determined from gestational weeks derived from the LMP-equivalent reference.

Example 3: IVF Day 5 transfer

Inputs: Transfer date = July 8, 2026; Embryo age = Day 5.

Computation outline: DueDate = TransferDate + (267 − 5) = TransferDate + 262 days. LMP_equivalent = TransferDate − (5 + 14) = TransferDate − 19 days, then compute gestational age from that baseline.

Result summary: IVF dating typically yields a precise due date based on recorded embryo age and transfer date, but clinical adjustments can still happen.

Common mistakes

  • Entering the last day (instead of the first day) of the last menstrual period for the LMP method.
  • Using a cycle length outside typical bounds without double-checking the number of days.
  • Mixing “ovulation date” and “conception date” without accounting for how they were estimated.
  • For IVF, selecting the wrong embryo age (Day 3 vs Day 5/6) when the clinic notes are unclear.
  • Comparing estimates without noting that early ultrasound dating can override calendar-based assumptions.

Quick tips

  • If your cycles vary, try the LMP method with your most typical cycle length rather than an outlier month.
  • For conception-based dating, use the most reliable date you have (confirmed ovulation is better than guesswork).
  • If you’re past the due date, focus on the “days past due” metric and discuss next steps with your clinician.
  • Use the milestones list to plan practical checkpoints, but treat scan windows as ranges—not exact days.
  • Re-check entries if results look off by weeks; a single month/date slip can shift the estimate significantly.

FAQ

How accurate is a due date calculator?
A due date calculator provides an estimate based on standard dating rules, not a guarantee of delivery on that exact day. Many pregnancies deliver within a window around the estimated due date. Accuracy depends on how precise your input is: IVF transfer dates are usually highly reliable, while LMP-based estimates can shift if cycle length varies or ovulation occurs earlier or later than average. Clinicians may adjust the due date based on early ultrasound measurements, especially if the scan suggests a different gestational age than the calendar estimate.
Why does cycle length change the LMP due date?
The standard LMP estimate assumes a 28-day cycle with ovulation around day 14. If your cycle is longer, ovulation often happens later; if shorter, it can happen earlier. This calculator applies a simple adjustment: it adds CycleLength − 28 days to the baseline 280-day estimate. It’s a practical correction that keeps the model consistent without requiring you to guess ovulation. If your cycles are highly irregular, the LMP method can still be useful, but it may differ more from ultrasound dating.
What if I don’t know my last menstrual period?
If you don’t know your LMP, consider using the Conception Date method if you have a reliable conception or ovulation date. If you conceived through IVF, the IVF/Transfer method is usually the best fit because it uses recorded clinical timing. Otherwise, your clinician may estimate gestational age using an early ultrasound scan, which can provide an updated due date. This calculator is most helpful when the input date is solid—so choose the method that matches the most trustworthy information you have.
Why can ultrasound due dates differ from LMP estimates?
Ultrasound dating, especially in the first trimester, estimates gestational age based on fetal measurements that correlate with typical growth patterns. If ovulation occurred earlier or later than the LMP model assumes, the fetus may measure “ahead” or “behind” compared with the calendar estimate. In that case, clinicians may revise the due date to align with ultrasound findings, since early growth can be a more consistent marker than cycle timing. Differences are common and don’t necessarily indicate a problem—often they reflect natural cycle variability.
How do you calculate gestational age from a conception date?
Gestational age is traditionally counted from the LMP, not from conception. To display weeks and days in that standard format, we convert your conception date into an LMP-equivalent date by subtracting 14 days. Then we count the number of days from that LMP-equivalent date to your local “today” date and convert it into weeks and remaining days. This uses the common assumption that conception happens about two weeks after the LMP in a typical cycle. It’s a standardized approach for consistent trimester and milestone calculations.
How is IVF due date dating different?
IVF dating relies on known clinical timing: the transfer date and embryo age (Day 3, Day 5, or Day 6). Because embryo development stage is recorded, the due date estimate can be more precise than LMP-based methods. This calculator uses a standard IVF rule: DueDate = TransferDate + (267 − EmbryoAgeDays). For gestational age, we compute an LMP-equivalent baseline by subtracting (EmbryoAgeDays + 14) days from the transfer date, then count forward to today. Clinics may still adjust dating based on medical records.
What does “full term” mean in the timeline?
“Full term” is commonly described as the period around 39–40 weeks of gestational age, when many pregnancies naturally reach a mature stage. The timeline in this calculator highlights a 39–40 week window as a practical planning marker, not an instruction. Some deliveries happen earlier, and some pregnancies continue beyond 40 weeks. If pregnancy extends to 41 weeks or later, clinicians often discuss additional monitoring and potential interventions. Always follow your care team’s guidance for timing and clinical decisions.
What if the calculator says my due date has passed?
If the estimated due date is in the past, the calculator will show how many days past due the estimate is. This can happen if the input date was earlier than intended, if your due date was updated clinically, or if you are genuinely beyond the estimated date. Late-term and post-term pregnancies are managed with individualized care, and many clinicians increase monitoring as pregnancy progresses. Re-check the date you entered and your method selection. If the estimate is correct, use the “days past due” value as a planning reference and consult your clinician.

Sources & references

  • Standard obstetric dating conventions (gestational age counted from LMP; 40 weeks baseline).
  • Common IVF dating approach using embryo age at transfer and transfer date to derive EDD.
  • Clinical milestone ranges (trimester boundaries and typical scan windows used for planning).

This page summarizes widely used clinical rules; your care team may apply different protocols based on your specific circumstances.

Accuracy, privacy, and care notes

  • Runs locally in your browser: calculations happen on your device for fast results.
  • Privacy-first: no input data is sent anywhere by this widget.
  • Rounding policy: day-level math only; weeks are whole weeks and remaining days are shown separately.
  • Last Updated: January 28, 2026

If your results differ from a clinic estimate, it’s often because ovulation timing varies or early ultrasound measurements lead to a revised due date.

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