A newborn baby is 0 weeks old on day one. By week 4, your baby is approximately 1 month old — though many parents note that "1 month" and "4 weeks" aren't exactly the same. The exact calculation matters more than you might think, especially for pediatric checkups, developmental milestones, and school admission deadlines.
Quick answer: Use our Age Calculator to get your baby's exact age in weeks and months instantly. Enter the date of birth and the current date — the calculator shows baby age in days, weeks, months, and years with no signup required.
Last Updated: June 2026 | Reviewed by EaseToolz Editorial Team
Baby Age Chart — Weeks to Months Conversion
| Baby Age (Weeks) | Baby Age (Months) | Approximate Stage |
|---|---|---|
| 0–1 | Newborn | First week |
| 2–4 | ~1 month | Newborn stage |
| 5–8 | ~2 months | Social smiling begins |
| 9–13 | ~3 months | Head control developing |
| 14–17 | ~4 months | Rolling attempts begin |
| 18–21 | ~5 months | Sitting with support |
| 22–26 | ~6 months | Solid foods introduction |
| 27–30 | ~7 months | Sitting independently |
| 31–35 | ~8 months | Crawling begins |
| 36–39 | ~9 months | Pulling to stand |
| 40–43 | ~10 months | Cruising along furniture |
| 44–47 | ~11 months | First steps possible |
| 48–52 | ~12 months / 1 year | First birthday |
Why "4 Weeks" ≠ "1 Month"
This confuses almost every new parent. Here is why:
- 4 weeks = 28 days
- 1 calendar month = 28, 29, 30, or 31 days (depending on the month)
So if your baby was born on January 15, they will be exactly 1 month old on February 15 — which is more than 4 weeks if February has 28 days (it is 31 days later, not 28).
Rule: Always count months by calendar date, not by 4-week blocks. A baby born on the 15th is 1 month old on the next 15th, 2 months old the following 15th, and so on.
This is why pediatricians use exact dates for milestones, not "week numbers" past the first few months.
How to Calculate Baby Age in Weeks
Step 1: Note the baby's date of birth (DOB).
Step 2: Count the exact number of days from DOB to today.
Step 3: Divide total days by 7.
Example:
- DOB: March 1, 2026
- Today: May 31, 2026
- Days elapsed: 91 days
- Baby age in weeks: 91 ÷ 7 = 13 weeks (with 0 days remainder)
- Baby age in months: approximately 3 months
The EaseToolz Baby Age Calculator does this automatically — just enter the birth date.
Corrected Age for Premature Babies
If your baby was born prematurely, pediatricians use corrected age (also called adjusted age) rather than chronological age for developmental milestone tracking.
Formula:
Corrected age = Chronological age − Weeks premature
Example:
- Baby born at 32 weeks (8 weeks premature)
- Chronological age: 6 months
- Corrected age: 6 months − 2 months = 4 months
Corrected age is used for milestones until approximately age 2 for most premature babies, though your pediatrician will guide the specific timeline.
Baby Age Milestones by Month
| Age | Key Milestones |
|---|---|
| 1 month | Lifts head briefly, startles at sounds, focuses on faces |
| 2 months | Follows objects visually, first social smiles |
| 3 months | Bats at objects, coos, head control improving |
| 4 months | Rolls front-to-back, laughs, grabs objects |
| 5 months | Sits with support, transfers objects hand to hand |
| 6 months | Sits momentarily unsupported, babbling begins |
| 7–9 months | Crawling, pulling to stand, object permanence |
| 10–12 months | Cruising, first words, pincer grasp |
| 12 months | Walking attempts, says 1–2 words, waves bye-bye |
These are general developmental guidelines. All babies develop at their own pace.
School Admission Age by Indian State (2026)
If you want to know when your baby is eligible for nursery or kindergarten admission, here are the cutoff ages across major Indian states:
| State | Nursery | LKG (Kindergarten) | Class 1 |
|---|---|---|---|
| Delhi | 3 years by March 31 | 4 years by March 31 | 5 years by March 31 |
| Maharashtra | 3 years by June 30 | 4 years by June 30 | 5 years by June 30 |
| Karnataka | 3 years by June 1 | 4 years by June 1 | 6 years by June 1 |
| Tamil Nadu | 3 years by June 30 | 4 years by June 30 | 5 years by June 30 |
| Uttar Pradesh | 3 years | 4 years | 6 years by April 1 |
| Gujarat | 3 years by June 15 | 4 years by June 15 | 6 years by June 15 |
Cutoff dates vary by school and academic year. Always verify with your local school.
The EaseToolz Age Calculator can tell you the exact date your baby meets any specific age requirement — just select a target date and check if they'll be old enough.
How Hospitals Calculate Newborn Age
In the first few weeks of life, babies are often described in days, not weeks:
- Day 0 = birth day
- Day 7 = 1 week old (exactly)
- Day 14 = 2 weeks old
- Day 21 = 3 weeks old
After 4 weeks, most parents switch to weeks and then months. After 12 months, most switch to years and months ("He's 1 year and 3 months").
Doctors and researchers switch to gestational weeks for very young babies — especially for premature infants — using weeks since the last menstrual period.
Baby Age in Months — First Two Years
| Months | Days | Baby's Age Said As |
|---|---|---|
| 1 month | ~30 days | "1 month old" |
| 2 months | ~61 days | "2 months old" |
| 3 months | ~91 days | "3 months old" |
| 6 months | ~183 days | "Half a year old" |
| 9 months | ~274 days | "9 months old" |
| 12 months | ~365 days | "1 year old" |
| 15 months | ~456 days | "1 year 3 months old" |
| 18 months | ~548 days | "1.5 years old" |
| 24 months | ~730 days | "2 years old" |
Common Questions
Q: How do I calculate my baby's age in weeks? Count the exact number of days from the date of birth to today, then divide by 7. For example, 70 days old = 10 weeks old. Use our Age Calculator for instant results.
Q: Is a 4-week-old baby 1 month old? Not exactly. Four weeks is 28 days, but one calendar month can be 28–31 days depending on the month. Pediatricians use calendar months (counting from the same date in each month) rather than 4-week blocks.
Q: How old is a baby in months at 100 days? 100 days is approximately 3 months and 1 week old (about 3.3 months). The exact month count depends on the birth month.
Q: At what age does a baby become a toddler? Most developmental frameworks define a toddler as 12–36 months (1–3 years old). The transition from infant to toddler typically coincides with independent walking, which usually begins between 9–15 months.
Q: My baby was born in December 2025 — when will they be eligible for school? This depends entirely on your state's cutoff dates and which academic year you're targeting. Use the Age Calculator to check if your baby will meet the age requirement for your school's admission month.
Q: How many weeks in 6 months? Approximately 26 weeks (6 × 4.33 weeks/month). The exact number varies by which 6 calendar months you're counting.
Calculate Your Baby's Exact Age
Use the EaseToolz Age Calculator to:
- Get exact age in days, weeks, months, and years
- Check school admission eligibility for any state cutoff date
- Find the exact date your baby reaches any milestone (100 days, 6 months, 1 year)
- Works for premature babies — just adjust the date
- No app download, no signup, completely free
Last Updated: June 2026 | Sources: American Academy of Pediatrics, WHO Child Growth Standards, Indian School Admission Guidelines 2026