How it works
How Pregnancy Due Date calculadora solves the problem
Think of Pregnancy Due Date calculadora as the back-of-the-envelope version of the calculation, only the envelope is a web page and the arithmetic is audited by our test suite.
A number is a prompt to talk to your GP, not a diagnosis. Rest 5 minutes before taking the reading — then work out the number and the rest of this page explains what the answer means.
Add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a regular 28-day cycle; dating ultrasounds at 11–13 weeks are the NHS gold standard.
The formula we run is EDD = LMP + 280 days (Naegele). You'll see each term laid out in the worked example below.
Seeing it on real numbers
A working example keeps the formula honest:
Add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a regular 28-day cycle; dating ultrasounds at 11–13 weeks are the NHS gold standard.
Every run comes back to EDD = LMP + 280 days (Naegele) — change the inputs, the structure of the answer stays.
Moments this tool earns its keep
Pregnancy Due Date calculadora is aimed at people arriving with questions like these:
- "Naegele rule"
- "Due date from lmp"
- "How far along am i"
- "Pregnancy trimester weeks"
- "What is pregnancy due date"
- "How to calculate pregnancy due date"
Where the number stops being useful
Every tool has an edge where it stops being the right answer. Pregnancy Due Date calculadora is no exception:
- For legally binding tax or medical decisions — cross-check with HMRC, NHS or a qualified professional.
- For very large or very small extremes the rounding error outgrows the useful precision.
- When the underlying rate or threshold has changed since the page was last reviewed — always verify with the primary source.
- When the input you have is already a derived figure (net of something) — feeding it in as "gross" will double-subtract.
Traps to steer around
Every time you work out the number for a new scenario, one of these creeps in — it's worth knowing them ahead of time.
- Assuming the UK and US versions of the same unit are interchangeable — they're not.
- Typing a comma where the tool expects a dot (or vice versa).
- Rounding early — particularly painful in percentages and compound growth.
- Ignoring the time window: a 'per year' answer makes no sense with a monthly input.
- Treating the answer as private: screenshots are fine, but the URL always reruns cleanly.
The sources behind the numbers
Where the maths needs an external authority, we cross-check against:
- NHS
- RCOG
- WHO
Works well alongside
If this question keeps coming up for you, the same cluster of tools usually comes next:
- Ovulation calculadora — Predict your fertile window and ovulation day based on cycle length and last period — uses the 14-days-before-next-period midpoint.
- Age calculadora — Work out your age in years, months, days and even total hours from your date of birth.
- Date Difference calculadora — Calculate the number of days, weeks, months or years between any two dates — including working days and UK bank holidays.
How we keep this accurate
Our calculadoras run on pure, unit-tested functions — the same logic lives in the browser and in the CI test suite. When tax rates, thresholds or official figures move, the update lands within 24 hours of the announcement. You can read the editorial policy and corrections policy.
Found an out-of-date number on Pregnancy Due Date calculadora or anywhere else in the Health toolkit? Send it to the editorial desk and we'll patch it. Or browse the full calculadora directory for the next tool you need.