Are Pregnancy Apps Accurate? What They Get Right and Wrong
Reviewed by Safi Allah Khan
Medically reviewed by: Safi Allah Khan · Written by the Momi team · Last updated 20 October 2026
Quick answer: Are pregnancy apps accurate? For dates, yes: counting weeks from your last period or due date is simple maths, so the result is as accurate as the date you enter. Use your dating-scan due date. Baby sizes are averages, not your baby. No app can tell you if a symptom is serious.
For how due date calculators work, see is a pregnancy calculator accurate?. This guide looks at apps as a whole: dates, sizes, content and tools.
What pregnancy apps calculate
| Feature | How it's worked out | How accurate |
|---|---|---|
| Due date | Last period + 280 days, or conception date + 266 days | As accurate as the date you enter; your provider may update it after a scan |
| Current week and trimester | Days since your last period | Exact maths; check whether the app shows "in week X" or "X weeks" |
| Weeks to go | Due date minus today | Exact maths, but only about 1 in 20 babies arrive on the due date |
| Baby size and weight | Average growth data for that week | An average; your baby may differ |
| Development milestones | Typical timing from medical sources | Typical, not guaranteed |
| Kick counter, contraction timer | Your taps | Accurate timing; interpretation needs your provider |
Why the due date matters most
ACOG says ultrasound measurement in the first trimester is the most accurate way to confirm or set the due date, and your provider may change your due date if a scan differs from your period-based date by more than a set amount. Royal Berkshire NHS notes that scan dating has a margin of about 5 days early in pregnancy. If your app's date isn't updated, every week, size and countdown will be off.
Tip: after your dating scan, change the due date in your app to the one your provider gives you. In Momi, you can set it from your last period or conception date, then update it.
Where app information comes from
Pregnancy apps vary a lot in where their health content comes from:
- Medical organizations: content based on ACOG, the NHS, WHO, CDC or Mayo Clinic
- In-house medical reviewers: a named doctor, midwife or nurse checks content
- User communities: forums and comments, which are personal experiences, not advice
- AI assistants: some newer apps use AI to answer questions; useful for general information, but they can't examine you
How to judge an app's accuracy
- Does it cite sources? Look for ACOG, NHS, WHO, CDC or Mayo Clinic.
- Is there a review date and reviewer? Medical content should be checked regularly.
- Does it let you change the due date? Essential after a scan.
- Does it explain week counting? Good apps make clear whether "week 12" means 11 or 12 weeks completed.
- Does it avoid diagnosing? Be wary of apps that suggest a symptom is "nothing to worry about".
- Does it handle loss and complications well? Consumer Reports' 2026 evaluation looked at how apps handled pregnancy loss, among other things.
Baby size: why it's an average
Apps show fruit, length and weight for each week. These come from average growth data. ACOG says the fetus is about 15 inches long and about 2.5 pounds at the end of week 28, for example, but healthy babies vary, and measurements such as crown-rump length (early) and crown-heel length (later) make numbers jump between weeks. See baby size by week.
What apps can't do
- Examine you or your baby. Only a check-up or scan can.
- Interpret your symptoms reliably. Bleeding, pain or headaches need a professional.
- Monitor your baby's heartbeat. The NHS advises against home dopplers and phone apps for listening to your baby's heartbeat.
- Replace kick count advice. A kick counter records movements; if they slow down or change, call your maternity unit immediately.
Talk to your provider
Use apps for what they do well: counting weeks, keeping notes, reminding you of appointments and timing kicks and contractions. Take questions from the app to your midwife or doctor, and always follow their advice over an app's.
How Momi sources its content
Momi works out your due date from your last period or conception date and shows your week, trimester, weeks to go and an approximate baby size, length and weight. On this website, every guide cites sources such as ACOG, the NHS, CDC, WHO and Mayo Clinic, with the date we checked them, and a medical review status. See our editorial policy.
How Momi helps
Momi keeps the maths simple and transparent: set your due date, update it after your scan, and follow along week by week. Log weight, appointments and medicine reminders, write in the diary, and use the kick counter and contraction timer when you need them.
Download Momi free on the App Store or Google Play. Free with ads; optional Premium.
Related: best pregnancy apps · due date calculator · can my due date change?
Sources
- ACOG, Committee Opinion 700: Methods for Estimating the Due Date
- ACOG, How Your Fetus Grows During Pregnancy
- ACOG, Ultrasound Exams
- NHS, 12-week scan
- Royal Berkshire NHS, Baby due dates and how it affects my care (PDF)
- NHS, Your baby's movements
- Consumer Reports via Quartz, The 4 best pregnancy tracking apps of 2026
Medical disclaimer: Momi and this website provide general information, not medical advice. Always talk to your doctor or midwife; in an emergency call your local emergency number.
FAQ
How accurate are pregnancy tracking apps?
The week counting is simple maths, so it's accurate as long as the due date you enter is right. Use the due date from your dating scan. Baby sizes and development notes are averages, and symptom information is only as reliable as the sources behind it.
Why does my app say a different week from my doctor?
Usually because the app is using your last period while your doctor has updated your due date after a scan, or because the app shows the week you're in rather than completed weeks. Change the due date in your app to match your provider's.
Is the baby size in pregnancy apps accurate?
It's an average, not your baby's measurement. Healthy babies vary, especially later in pregnancy. Only an ultrasound can estimate your baby's actual size, and even scan estimates have a margin of error.
Can a pregnancy app tell me if something is wrong?
No. An app can't examine you or your baby. Use it for information and tracking, not to decide whether a symptom is serious. Call your midwife or doctor about bleeding, severe pain, fluid leaking, reduced movements or anything that worries you.
How do I know if a pregnancy app's information is reliable?
Look for content that cites organizations such as ACOG, the NHS, WHO or Mayo Clinic, shows when it was last reviewed, and names who wrote or reviewed it. Be cautious with apps that make medical claims without sources.
Related guides
Track this in Momi
Momi is a free pregnancy tracker app for iPhone and Android that follows pregnancy week by week, estimates the due date, and keeps a pregnancy journal, weight log, kick counter and contraction timer in one place.
