How Old Is My Baby? Free Baby Age Calculator

Enter your baby’s birth date:


  • Your baby is:
  • or
  • or
  • and

Baby age in weeks, months and days – at a glance

Newborn weeks, calendar months, “corrected age” – keeping track of how old your baby really is can be confusing. This free Baby Age Calculator shows you your baby’s age in weeks, months and days based on their date of birth, so you always have a clear number for check-ups, clothing, and routines.

Simply enter your baby’s date of birth and tap “Calculate”. The tool will instantly tell you:

  • how old your baby is in days and weeks
  • how old your baby is in months
  • which age range this corresponds to for many everyday decisions

How the Baby Age Calculator works

The calculator uses your baby’s date of birth and today’s date to work out their exact age. It counts the total number of days and weeks since birth and converts this into whole months plus remaining days. This gives you a practical view for everyday life: “10 weeks old”, “4 months old”, or “7 months and 5 days”.

This is especially useful when:

  • reading baby clothing labels that use age ranges (0–3 months, 3–6 months, 6–9 months …)
  • following sleep and feeding guides that are organised by age
  • tracking routines and milestones from week to week

Always remember: every baby develops at their own pace. Age is just one helpful input when you make decisions for your baby.

FAQ: Questions about baby age and this calculator

How do I calculate my baby’s age correctly?

The simplest way is to start from your baby’s date of birth and count forward to today. This Baby Age Calculator does that for you automatically and shows the result in days, weeks and months, so you do not have to count manually.

Why does my baby’s age look different in weeks and months?

Months are not all the same length, so the number of weeks and the number of months won’t match perfectly. For example, 3 months is often somewhere between 12 and 13 weeks. This is normal. Many parents use weeks during the newborn phase and then switch to months later in the first year.

Should I use the due date or the birth date?

For most everyday situations, such as clothing, play and routines, parents use the birth date to calculate age. Some health professionals also talk about a corrected age for babies who were born early. If you are unsure which age to use for medical or developmental questions, follow the guidance of your midwife or paediatrician.

What is corrected age for premature babies?

Corrected age is the age your baby would be if they had been born on their original due date. It can be helpful when discussing growth and development with health professionals. This tool uses the birth date, so always check with your care team if you have questions about corrected age or development.

Why do I need to know my baby’s age so exactly?

Knowing your baby’s age in weeks or months makes it easier to use many everyday guides: baby clothing sizes, sleep routines, feeding schedules and activity ideas. It gives you a starting point, but your baby’s cues are always more important than any chart or schedule.

Is this Baby Age Calculator medical advice?

No. This calculator is for general information only and is not a medical tool. It does not assess growth or development and cannot replace professional advice. Always speak to your midwife, paediatrician or health visitor if you have questions or concerns about your baby.

What to do after you know your baby’s age

Once you know how old your baby is, you can use it as a helpful input for everyday decisions about clothing and routines:

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