Pregnancy Month Calculator
Convert weeks pregnant into months of pregnancy. Free, private and instant.
How to use the Pregnancy Month Calculator
- Choose work out from my: Last period date or Due date.
- Answer any extra questions that appear for your choices.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Pregnancy Month Calculator
Doctors count pregnancy in weeks, but many people think in months. This calculator converts your weeks pregnant into months, shows which of the nine months you are in and lists the weeks that make up each month.
Also known as: how many months pregnant am I, pregnancy weeks to months, months pregnant calculator, pregnancy month chart.
Worked example
Dates in this example are worked out as if today were 5 Nov 2026.
- Work out from my: Last period date
- First day of your last period: 18 Jul 2026
You are in: 4 months (month 4 of 9) (15 weeks 5 days pregnant). At 15 weeks 5 days you are in your fourth month, with 3 full months completed. A 40-week pregnancy is about 9 months plus 1 week, not 10 months.
- Current month: Month 4 of 9
- Full months completed: 3
- Pregnant for: 15 weeks 5 days
- Months left (approx.): 5.6
Formula and cut-offs
Month 1 = weeks 1-4, month 2 = weeks 5-8, month 3 = weeks 9-13, month 4 = weeks 14-17, month 5 = weeks 18-21, month 6 = weeks 22-26, month 7 = weeks 27-30, month 8 = weeks 31-35, month 9 = weeks 36-40.
Frequently asked questions
How many months is 20 weeks pregnant?
Twenty weeks is about 4.6 months, the start of month 5.
Is pregnancy 9 or 10 months?
Forty weeks is about 9 months and 1 week. It is 9 calendar months from conception, and 10 lunar months of 4 weeks from the last period.
Why do doctors use weeks?
Weeks are more precise than months, which vary in length.
Sources and references
- ACOG Committee Opinion 700 - Methods for estimating the due date
- Institute of Medicine (2009) - Weight Gain During Pregnancy: Reexamining the Guidelines
- NHS - Pregnancy guide
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.