Pregnancy Due Date Calculator
Estimate your due date using Naegele's rule from your last menstrual period date.
How to use this tool
- 1Enter the first day of your last menstrual period (LMP).
- 2The estimated due date, conception date, and trimester start dates appear instantly.
About Pregnancy Due Date Calculator
This due date calculator estimates the expected delivery date, conception window, and trimester start dates from the first day of your last menstrual period using Naegele's rule — the standard clinical formula used in obstetric practice.
Early pregnancy questions arise before a first clinical appointment. Knowing an approximate due date helps with scheduling, planning leave, and understanding which trimester a pregnancy is currently in. Having an estimate in hand before the first ultrasound also gives context for the dating scan result.
Enter the first day of your last menstrual period. The estimated due date, approximate conception date, and the start dates for the second and third trimesters appear instantly. Processing runs in the browser — no upload, no account, no data stored.
Naegele's rule adds 280 days (40 weeks) to the LMP date and assumes a 28-day cycle with ovulation on day 14. If your cycle is consistently shorter or longer than 28 days, the estimate will be off by roughly the same number of days as the cycle difference. Clinical dating by ultrasound — particularly a first-trimester crown-rump length measurement — is more accurate than LMP-based calculation and will supersede this estimate if the two disagree significantly.
This tool provides a planning estimate, not medical advice. Gestational age, due date, and trimester boundaries should be confirmed with a qualified healthcare provider. Pregnancy outcomes depend on many factors beyond gestational timing, and no calculator replaces clinical assessment. Use this estimate for personal planning only, and discuss any concerns about dates or development with your midwife or obstetrician.
Frequently asked questions
Different tools use different definitions and parsers, so small gaps are common. Pregnancy Due Date Calculator applies standard formulas evaluated in JavaScript with one consistent browser-side rule set. Hidden characters, stricter syntax, or a different tokenizer usually explain the mismatch. Reduce the input to a minimal sample, then add pieces back until the difference appears. Match the rule your destination actually enforces.
Treat the error as a signal that this environment is stricter or configured differently. Browser APIs reject malformed structures early instead of guessing. Convert to a boring intermediate when it helps—plain UTF-8 text, PNG, WAV, or an unlocked PDF—then retry. If the intermediate works, the original encoding was the problem. Keep that minimal sample for the next regression check.
Runtimes disagree even when feature names match. Locales, parser strictness, codec builds, and library versions differ between your browser and CI. Export the exact bytes from Pregnancy Due Date Calculator, hash them, and compare in the pipeline. Align normalization steps so both systems see the same input. Use the browser result as a reference artifact, then make CI match it.
Desktop apps win on deep feature sets, batch farms, and specialized hardware paths. Pregnancy Due Date Calculator wins on zero install, private local processing, and speed for the everyday job on this page. Choose desktop software for multi-hour editorial work or exotic edge formats. Choose this tool when you need a correct result quickly without uploading. Many people do a quick pass here first, then open the heavy suite only if an edge case demands it.
Prefer Pregnancy Due Date Calculator whenever the input is personal, unpublished, customer-owned, or under NDA, because the core transform stays in your browser via standard formulas evaluated in JavaScript. Cloud services can still help for formats your browser truly cannot decode, but you must trust their retention policy. Strip secrets before any upload. Privacy is usually the reason to stay local—not a longer marketing checklist.
Start from the best original input you still have. Change only what the destination requires. Prefer lossless intermediates when you must convert twice. Because the tool is local, iterate in small steps: tweak one setting, re-run, compare. Spot-check a short sample before batching anything important.
No account is required for normal use. The core pregnancy due date calculator transform runs in your browser on your device using standard formulas evaluated in JavaScript. You get on-screen output, a copy action, or a download without a mandatory ToolBrigade upload for that step. Keep your browser updated. A few lookup utilities may call public reference APIs for live fields only—they still do not need your private documents.
Lighter text, code, calculator, and many image jobs work on modern phones. Large video encodes and huge PDFs are happier on a plugged-in laptop with more RAM. Fully client-side flows can continue offline once scripts are cached; live lookups still need network. If a run seems stuck, try a smaller sample, free memory by closing tabs, and confirm the input is not truncated. Prove the path on a short fixture before blaming the algorithm.
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