Last updated
Adds 280 days (40 weeks) to a first-day-of-last-period date using a common rule-of-thumb. Ultrasound dating and provider judgment override this estimate.
Quick answer: Due Date Calculator (LMP)
Classic LMP + 280 calendar days while reminding everyone ultrasound dating moves the official sticker.
Example: Jan 10 LMP → mid-October EDD on the napkin calendar before the 8-week scan adjusts it.
Calculations follow the documented formula on this page; rounding and input units can change the last digit-treat outputs as educational estimates unless you reconcile with source systems.
* This is an estimate. Actual amounts may vary slightly based on input assumptions.
Irregular ovulation, hormonal contraception gaps, and IVF transfer dates all break naive LMP math - the tool is a first phone-call estimate.
Adds 280 days (40 weeks) to a first-day-of-last-period date using a common rule-of-thumb. Ultrasound dating and provider judgment override this estimate.
Inputs on this page: First day of last menstrual period. Assumptions stay visible so you can reproduce the figure elsewhere.
Long-form walkthroughs that pair well with this calculator. When you need narrative context beyond the live fields, start here and return to the tool to plug in your own numbers.
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Read guide →People who care about due date calculator use Due Date Calculator (LMP) as a planning sandbox: Naegele’s rule ignores cycle length - add/subtract if you track ovulation.
Continue in the Calculators category hub, the Utility tools collection, or the glossary. Related calculators in this session: Date Difference Calculator, Age Calculator, Anxiety Level Self-Assessment (GAD-7 style), Life Expectancy Calculator, BMI for Children Calculator, Percentage Calculator.
The Formula
EDD ≈ LMP + 280 days (calendar)| This tool | EDD ≈ LMP + 280 days (calendar) |
|---|---|
| Related intent: due date calculator | See paired tools for due date calculator-each page documents its own core relationship next to the live form. |
| Related intent: pregnancy due date calculator lmp | See paired tools for pregnancy due date calculator lmp-each page documents its own core relationship next to the live form. |
Core relationship for Due Date Calculator (LMP):
EDD ≈ LMP + 280 days (calendar)
Worked check: Jan 10 LMP → mid-October EDD on the napkin calendar before the 8-week scan adjusts it.
Keep the same assumptions and open a neighbor calculator when your question branches: Date Difference Calculator, Age Calculator, Anxiety Level Self-Assessment (GAD-7 style), Life Expectancy Calculator. Each page documents its own formula beside the fields.
Learning links: Methodology · Editorial policy · Glossary
Jan 10 LMP → mid-October EDD on the napkin calendar before the 8-week scan adjusts it.
Re-enter the same numbers in the calculator above to confirm the page math matches the interactive result.
People who care about due date calculator use Due Date Calculator (LMP) as a planning sandbox: Naegele’s rule ignores cycle length - add/subtract if you track ovulation.
Instant response
Run Due Date Calculator (LMP) in the browser and read the breakdown beside the form.
Transparent formula
The formula and worked example on this page match what the calculator uses.
Privacy friendly
No account required; inputs stay in your session unless you choose to share them.
Cross-device ready
Layout works on mobile, tablet, and desktop for the same field labels.
Official references for context. Calculator outputs are planning estimates—confirm material decisions with the primary authority or a qualified professional. See our methodology and editorial policy.
Reviewed July 18, 2026 · Content stamp 2026-07-18
Click a question to expand the answer.
No. Only your maternity provider can confirm gestational age and due date.
It is a common 40-week convention from LMP; cycle length and ovulation vary.
LMP-based EDD is less reliable - rely on early ultrasound dating.
IVF often uses embryo transfer date or retrieval - ask your clinic for the official EDD.
Use ISO YYYY-MM-DD to avoid month/day confusion.
Classic LMP + 280 calendar days while reminding everyone ultrasound dating moves the official sticker.
Jan 10 LMP → mid-October EDD on the napkin calendar before the 8-week scan adjusts it.
Naegele’s rule ignores cycle length - add/subtract if you track ovulation. Postpartum contraception counseling still needs gestational age from charts, not this page. Travel insurance and workplace leave paperwork want the clinic letterhead date.
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Reviewed by Toollabz Editorial
Product editor | Last reviewed July 18, 2026
See methodology and editorial policy.