Why calculate your baby's exact age?
In the first year, a baby's age in weeks and months matters far more than it ever will again. It shapes when vaccinations are due, when growth is checked, when solid foods are introduced, and which developmental milestones your baby is moving toward. A rough "about six months" can hide a lot: a baby at 22 weeks and a baby at 26 weeks are in genuinely different stages, with different feeding, sleep and play needs. Knowing the exact age makes it easier to understand what is typical right now — and what to look forward to next.
It also helps you speak the same language as your paediatrician, who works in completed weeks and months, and it lets a tracker line up guidance to precisely where your baby is. That is why this page pairs an exact calculation with an age-matched dashboard, the week-by-week guides and the month-by-month guides.
Baby age in weeks vs months: which should you use?
Both are useful, and they answer slightly different questions. Weeks are the most precise unit in early infancy, when change is fastest — they are how vaccine schedules and many growth checks are timed. Months are easier for everyday conversation and for milestones, which are usually described by month ("around six months", "by twelve months").
A simple rule of thumb: think in weeks for the first few months and for anything medical, and in months for milestones and the bigger picture. Because months vary in length, four weeks is not exactly one month — over a year those extra days add up, which is why the calculator counts real calendar dates rather than assuming every month is 30 days.
How to calculate a baby's age by date of birth
The method is simple, and the calculator above does it instantly:
- Days: count the whole days between the date of birth and today.
- Weeks: divide the total days by seven — the whole number is completed weeks, and the remainder is the extra days.
- Months: count completed calendar months, so a baby born on the 12th becomes a month older on the 12th of the next month.
Doctors count completed units: a baby is "six months" until the day they complete seven months, not on the day they begin the sixth month. The calculator follows exactly this convention and shows the leftover days so nothing is rounded away.
Baby age in weeks to months: a quick reference
Because four weeks is slightly less than one calendar month, weeks and months drift apart over the year. This quick reference shows the approximate age in months for common week counts — the calculator above always gives your baby's exact figure:
- 4 weeks ≈ about 1 month
- 8 weeks ≈ about 2 months
- 13 weeks ≈ about 3 months
- 17 weeks ≈ about 4 months
- 22 weeks ≈ about 5 months
- 26 weeks ≈ about 6 months
- 30 weeks ≈ about 7 months
- 35 weeks ≈ about 8 months
- 39 weeks ≈ about 9 months
- 43 weeks ≈ about 10 months
- 48 weeks ≈ about 11 months
- 52 weeks ≈ about 12 months (first birthday)
These are rounded guides for quick mental maths. Health professionals and our week-by-week guides use exact completed weeks, which is what the calculator reports.
How accurate is this baby age calculator?
The age calculation is exact: it counts the real calendar days, weeks and months between the date of birth and today, handling leap years and the differing lengths of each month automatically. It works entirely in your browser at your device's local date, so the result matches the calendar day you actually see. The milestones, snapshot and vaccination timing are general, age-based guidance to help you know what is typical — not a personalised assessment of your individual child.
Chronological age vs corrected age
Chronological age is counted from the day your baby was born. Corrected (adjusted) age is counted from the due date and is used for babies born prematurely. To find corrected age, subtract the number of weeks your baby was born early from their chronological age.
Premature babies and adjusted age
For example, a baby born eight weeks early who is six months old on the calendar has a corrected age of about four months — and their development is usually compared against that four-month stage. Paediatricians typically use corrected age when looking at milestones and growth until around age two, after which most children have caught up. If your baby was born early, ask your doctor which age to use, be gentle with comparisons, and remember that catch-up varies a great deal from baby to baby.
Growth in the first year
Growth is best followed as a trend on the WHO growth chart rather than a single reading. Many babies lose a little weight in the first days, regain their birth weight by around two weeks, roughly double it by five to six months, and grow more slowly in the second half of the year as they become more active. Weight, length and head circumference are all plotted at routine check-ups; what matters most is a steady curve, not a specific percentile. Crossing centile lines up or down can be normal, but it is always worth mentioning to your paediatrician.
Development and milestones
Enter a date of birth above and the dashboard shows the milestones that are typical around now, framed as ranges rather than deadlines. The broad shape of the first year looks like this:
- 0–3 months: feeding on demand, social smiles, cooing, following faces, and steadier head control.
- 3–6 months: rolling, reaching and grabbing, laughing, and sitting with support.
- 6–9 months: sitting steadily, first tastes of solids, responding to their name, and babbling.
- 9–12 months: crawling, pulling to stand, cruising, gestures like waving, and self-feeding finger foods.
Every one of these varies widely between healthy babies. You can follow each week in detail in the week-by-week development guides, and keep a private record in the milestone tracker.
Vaccinations in the first year
In India, the National Immunization Schedule and the Indian Academy of Pediatrics schedule place vaccines at birth, then around 6, 10 and 14 weeks, at 6 and 9 months, and around 12 months, with boosters continuing into the second year. The calculator highlights the next likely vaccine for your baby's age so you can plan ahead — but the exact dates, doses and brands are always your paediatrician's call.
Sleep by age
Sleep changes dramatically across the first year. Newborns sleep around 14–17 hours in short bursts; by 4–11 months many babies sleep around 12–15 hours with two or three naps; toddlers need roughly 11–14 hours including a nap. Night waking is normal, and short "regressions" often coincide with developmental leaps or teething. Safe sleep is the constant: always on the back, on a firm flat surface, with nothing loose in the cot. The baby sleep guide covers safe sleep and gentle routines in depth.
Feeding by age
Milk — breast or formula — is the main source of nutrition for the whole first year. Solid foods usually begin around six months, when a baby can sit with support, hold their head steady and shows interest in food. Start with smooth or soft-mashed foods and safe finger foods, introduce common allergens one at a time, and avoid added salt, sugar, honey and whole nuts. The baby feeding guide walks through milk, first solids, textures and safety stage by stage.
Play and learning by age
Play is how babies learn, and the best toy is usually you. In the early months, face-to-face talking, singing and tummy time do the heavy lifting. From the middle of the year, reaching, grabbing, peekaboo and simple cause-and-effect toys support coordination and early thinking. Toward the first birthday, naming objects, encouraging gestures and give-and-take games build communication. Keep it simple, follow your baby's lead, and let repetition do its work.
Baby safety by age
Safety priorities shift as your baby becomes more mobile. Early on, safe sleep and never leaving a baby unattended on a raised surface come first. As rolling and grabbing begin, clear small objects and keep hot drinks away. Once pulling up and cruising start, babyproofing becomes essential: anchor furniture and TVs, use stair gates, cover sockets, and store medicines and cleaning products out of reach. Introduce foods in choke-safe shapes and always supervise eating.
Doctor visits and health checks
Routine check-ups in the first year are a chance to plot growth, review development, give scheduled vaccines and ask questions. Keeping a running list of questions helps — the appointment tracker and baby tracker make it easy to arrive prepared. Bring your growth records and immunisation card to each visit, and never hesitate to book an extra appointment if something worries you between checks.
Common concerns — and reassurance
Some of the most common worries — a baby who hasn't rolled, crawled or spoken "on time", who wakes often at night, or who eats little during a growth dip — usually reflect the wide range of normal rather than a problem. Milestones are averages with broad windows, and healthy babies vary enormously. Comparing with other babies rarely helps; following your own baby's trend over time, and trusting your instincts, does.
When to seek advice
It is worth checking in with your paediatrician if your baby loses a skill they previously had, if you have a persistent gut feeling that something is not right, or if you have specific concerns about movement, hearing, vision, feeding or communication. Seek urgent care for a high fever in a young infant, difficulty breathing, persistent vomiting, poor feeding or unusual drowsiness. Trust your instincts — asking is always reasonable, and this calculator is a starting point for conversation, never a substitute for it.
What comes next: toddlerhood
Around the first birthday, the week-by-week journey gives way to toddlerhood — first steps, first words and a burst of independence. From about 13 months, follow the month-by-month guides and the toddler development guides. The calculator keeps working for older children too, showing exact age and stage-appropriate guidance well beyond the first year.