Pregnancy Calculator

What this pregnancy calculator does

This calculator estimates the pregnancy timeline from a due date, last period, ultrasound, conception date, or IVF transfer date. It shows the estimated due date, likely conception date, current gestational week, trimester, and the date range for each trimester.

Gestational age is counted from the first day of the last menstrual period. That is why the timeline starts about two weeks before conception.

How to use this calculator

1. Choose what you are basing the estimate on.
2. Enter the relevant date.
3. Add cycle length, ultrasound gestational age, or embryo age if the mode asks for it.
4. Click Calculate to see the timeline.

The default example uses today's date as the last period and a 28-day cycle.

Pregnancy timeline formulas

Due date (last period) = LMP + 280 days + (cycle length − 28)
Due date (conception)  = conception + 266 days
Due date (ultrasound)  = scan date + (280 − gestational age in days)
Due date (IVF)         = transfer date + (266 − embryo age)
Conception date        = due date − 266 days
Gestational age today  = 280 days − days until due date

The first trimester is usually weeks 1–13, the second is weeks 14–27, and the third is weeks 28–40. The table shows the corresponding date ranges.

What the results mean

• Due date: the estimated delivery date.
• Likely conception date: the due date minus 266 days.
• Current week: gestational age at today's date.
• Trimester: the current stage of pregnancy.
• Trimester ranges: the date window for each trimester.

The conception date is an estimate. Sperm can survive several days, and the exact day of conception is rarely known.

Assumptions and limitations

The calculator assumes a valid date and a normal pregnancy timeline. It does not replace clinical dating, ultrasound interpretation, prenatal care, or medical advice. It does not account for twins, growth restriction, preterm delivery, or medical conditions.

If the due date is in the past or the date is invalid, the calculator will not produce a meaningful timeline.

Frequently asked questions

Why does the pregnancy start before conception?

Gestational age is measured from the last period, not from the day of conception. The two-week difference is standard in prenatal care.

Which date should I use?

Use the date your clinician is using. If you have an early ultrasound, its dating may be more accurate than the last-period date.

Is the conception date exact?

No. It is a calculated estimate based on a 266-day interval. The actual conception window can span several days.

Does this work for IVF?

Yes. Choose the IVF mode and the embryo age at transfer. The calculator adjusts the due date accordingly.

Reference table

Pregnancy milestones by week

Dates are estimates based on a 40-week pregnancy from the last menstrual period. Ultrasound dating and provider assessment control.

Source

References:

• ACOG — Calculating your due date
• NICHD — Pregnancy

Disclaimer

This calculator is for informational and educational purposes only. It is not prenatal care or medical advice. Confirm your timeline with a qualified obstetric clinician.