Simple calculators for new and expecting parents
Free, fast and private. Nothing you enter leaves your device.
Little Numbers answers the questions that come up again and again when you are trying to conceive, pregnant or caring for a baby. Each calculator gives a clear answer in a few seconds, explains how it was worked out and, where it relies on medical guidance, lists its sources.
Trying to conceive and pregnancy
Ovulation Calculator
Estimate your fertile window and next three cycles.
Due Date Calculator
Estimate your due date and see key pregnancy milestones.
Pregnancy Week Calculator
How many weeks pregnant you are today, with trimester and month.
Conception Date Calculator
Estimate when you conceived, from your due date, period or baby's birthday.
Your baby's first years
Baby Age Calculator
Exact age in months, weeks and days, with corrected age for preemies.
Growth Percentile Calculator
Weight, length and head size percentiles on the WHO growth charts.
Baby Sleep Schedule
Wake windows and a sample nap schedule by age.
Formula Amount Calculator
How much formula per day and per feed, by baby's weight.
Diaper Stock Calculator
How many diapers you need for the next weeks or months.
Not sure where to start?
- Trying for a baby: the ovulation calculator estimates your fertile window for the next three cycles.
- Just found out you are pregnant: get your date from the due date calculator, then see how far along you are with the pregnancy week calculator.
- Wondering when it happened: the conception date calculator works back from your due date or your baby's birthday.
- Your baby has arrived: check their exact age in weeks and months, see where they are on the growth charts, build a nap and bedtime schedule, and plan formula amounts and diaper supplies.
Why parents use Little Numbers
Private by design
Every calculation runs in your browser. The dates and numbers you type are never sent to us or stored anywhere.
Based on trusted guidance
The methods follow published guidance from organizations such as ACOG, the American Academy of Pediatrics and the NHS. Pages that rely on medical guidance list their sources.
Free, with no sign-up
There is no account to create, no app to install and no email to hand over. Use the calculators as often as you like.
Math you can check
Each page explains how its answer is worked out, and the calculations are covered by automated tests, including awkward cases like leap years.
Common questions
Are the calculators really free?
Yes. Every calculator is free to use, with no account, no sign-up and no limit on how often you use it.
Do you save the dates and numbers I enter?
No. The calculations happen in your own browser, so what you type never leaves your device and is gone when you close the page.
How accurate are the results?
They are estimates based on standard, widely used methods, such as Naegele's rule for due dates. They cannot take your personal medical history into account, so always follow the advice of your doctor, midwife or pediatrician.
Can I use the calculators on my phone?
Yes. The site is built to work well on phones and runs in any modern browser. You can also add it to your home screen for quick access.