Pregnancy & Family

Pregnancy week calculator

Week of pregnancy and calculated date according to the 280-day model.

Updated on Apr 21, 2026 Calculator, calculation path and examples on one page

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Calculator

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Calculation path

Step by step

  1. Set the starting date

    Formula: Standard model with 280 days

    Result: Dec 10, 2025

  2. Counting days since the beginning

    Result: 132

  3. Derive weeks and days

    Result: Pregnancy week 19 + 6

Instructions

How to use this calculator correctly

How to use the calculator

  • Choose a period or date as a starting point.
  • Enter the reference date and today's date.

Limits of the calculation

  • The model assumes a standard cycle and does not replace medical dating.

Common mistakes

  • Confusing the first day of the last period with ovulation.

Related guide: Better understand week of pregnancy, ovulation and fertile days

Examples

Typical calculations

Typical standard case.

From the last period

week of pregnancy: Week 14 + 0 of pregnancy

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Recalculation from the calculated date.

From the appointment

week of pregnancy: Week 14 + 0 of pregnancy

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Already more advanced.

Early start of pregnancy

week of pregnancy: Pregnancy week 19 + 6

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FAQ

Frequently asked questions

How does the pregnancy week calculator calculate?

With the standard model of 280 days from the first day of the last period.

Is the birth date binding?

No, it is just a mathematical guideline.

Can I also calculate backwards from the calculated date?

Yes, there is a mode for this with the date of birth as the starting point.

Why may medical dating differ?

Cycle length, ovulation and ultrasound findings may lead to different assessments.

Is the model accurate even with irregular cycles?

Only limited. With irregular cycles the deviation is often larger.

Related calculators

Continue seamlessly

Ovulation calculator

Calculate ovulation and fertile phase approximately from cycle start and cycle length.

Sources and notes

Rule status and context

methodology
280 days from the first day of the last period.