Which date should I use in LMP mode?
Use the first day of the last menstrual period. The calculator then applies the 280-day dating path and, if needed, adjusts the estimate by the difference between the entered cycle length and a 28-day cycle.
Estimate and plan
Pregnancy Due Date Calculator
Use this Pregnancy Due Date Calculator as an online due date and gestational age estimate tool with LMP mode, conception mode, cycle-length adjustment, and trimester output.
Health & FitnessPublished Mar 13, 2026Last reviewed Mar 13, 2026
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How to use Pregnancy Due Date Calculator
- 1
Choose the dating method you actually know
Start with LMP when you know the first day of the last menstrual period, or switch to conception mode when the conception date is the better anchor.
- 2
Enter the date and, for LMP mode, confirm cycle length
LMP mode includes the cycle-length adjustment because not every cycle is exactly 28 days. Conception mode keeps the form narrower when conception timing is the better reference.
- 3
Review due date, gestational age, and trimester together
The result card shows the estimate in one place so you can see the timeline clearly, while the limits panel keeps the estimate-only framing visible.
Workflow
Use Pregnancy Due Date Calculator when you need one clear timeline estimate from the information you have today
Pregnancy Due Date Calculator is built for a common early question: based on the dates available right now, what is the estimated due date, how far along is the pregnancy, and which trimester does that place the timeline in? That is useful when you need orientation quickly and want one online result card instead of calculating each piece by hand.
The page keeps the workflow deliberately simple by separating LMP and conception mode. That matters because the right anchor depends on what you actually know. When the known date changes, the explanation on the page changes with it, so the route stays readable instead of acting like one dating method fits every situation equally well.
How it works
LMP uses 280 days plus cycle adjustment, while conception uses 266 days and a gestational-age alignment offset
In LMP mode, the estimated due date is calculated as 280 days after the last menstrual period, then adjusted by the difference between the entered cycle length and a 28-day cycle. In conception mode, the estimate is 266 days after conception. The gestational-age path is also explicit: LMP mode measures from the LMP date itself, while conception mode adds 14 days to stay aligned with the standard clinical pregnancy timeline.
Trimester boundaries are fixed in one shared constant set, which keeps the day transitions stable. That means the same input will not drift between trimesters because of hidden date logic changes or locale-specific calendar behavior.
Limits
This due date result is an estimate and may change with provider dating or ultrasound
Pregnancy Due Date Calculator is intentionally framed as an estimate only. It does not diagnose complications, interpret symptoms, replace prenatal care, or settle questions that depend on provider dating. Early ultrasound findings, clinician review, and other medical context can change the estimated due date, even when the initial date entry was correct.
That limit is especially important because pregnancy dating feels precise on a screen. The page counters that impression on purpose. It provides a practical estimate, but it also keeps the limits panel visible so users understand that urgent symptoms, bleeding, pain, or uncertainty about dating belong with a healthcare professional rather than a website result.
Use cases
Practical cases where an estimated due date and gestational age are helpful
An estimated due date can be helpful when you are organizing appointments, framing a conversation, or sanity-checking a timeline after entering the most relevant known date. The trimester label is also useful in plain-language planning because it adds context that a raw gestational-age number does not always communicate by itself.
This tool is not the right fit when the real need is medical interpretation, emergency guidance, or official dating confirmation. Use it when the job is timeline orientation from known dates, and move to provider guidance when the decision depends on something more clinical than an estimate.
Frequently asked questions
How does conception mode handle gestational age?
Conception mode estimates due date as 266 days after conception, then adds 14 days when showing gestational age so the timeline stays aligned with the standard clinical pregnancy framework rather than treating conception day as 0 weeks 0 days.
Can this estimate change later?
Yes. The result is an estimate only. Provider dating and early ultrasound can change the due date, which is why the page does not present the output as a final medical answer or a replacement for prenatal care.
What cycle length can I enter?
LMP mode accepts cycle length from 21 to 35 days. That keeps the adjustment within the supported range for this version instead of letting implausible or incomplete values quietly distort the estimate.
Is this tool appropriate for urgent symptoms?
No. If there is bleeding, pain, sudden swelling, fainting, or any urgent concern, a website estimate is not the right next step. The calculator is for timeline orientation only and does not replace medical advice or urgent evaluation.