3-Month-Old Baby Weight: What’s Normal and What to Watch For

When we talk about 3-month-old baby weight, the typical mass of an infant at three months of age, used to track healthy growth patterns. It’s not about hitting a number—it’s about seeing consistent progress over time. Most babies in the UK gain about 140 to 200 grams a week during the first few months. By three months, many weigh between 5.5 and 6.5 kilograms, but that’s just a guide. Some babies are born bigger, some smaller, and that’s perfectly normal. What matters most is that your baby is growing steadily along their own curve, not comparing them to someone else’s.

Baby growth chart, a tool used by health professionals to track a child’s weight, length, and head circumference over time is your real friend here. Your health visitor will plot your baby’s measurements at check-ups, and if they’re following their own line—whether it’s the 10th or the 90th percentile—you’re doing great. Growth isn’t a race. It’s a quiet, steady journey. If your baby was born early or had a low birth weight, their growth will be tracked from their due date, not their actual birth date. That’s called corrected age, and it’s key to understanding their progress.

Infant development, the physical, cognitive, and social changes babies go through in their first year doesn’t just show up in weight. At three months, you’ll likely see your baby smiling more, holding their head up, and reaching for toys. These milestones often go hand-in-hand with healthy feeding and weight gain. If your baby is feeding well—whether breast or bottle—and seems alert, content, and making wet diapers regularly, their weight is probably where it needs to be.

Don’t panic if your baby’s weight dips slightly after birth. It’s common to lose up to 10% in the first few days. Most babies bounce back by two weeks. But if your baby isn’t gaining weight after that, or if they seem lethargic, aren’t feeding well, or have fewer than six wet nappies a day, it’s worth a quick chat with your health visitor. Sometimes it’s just a latch issue, a growth spurt delay, or a temporary dip in appetite. Other times, it’s a sign to check in.

There’s no magic number for a 3-month-old baby weight. What you’re really looking for is consistency. Your baby’s growth pattern over weeks and months tells the real story—not a single number on a scale. Trust your instincts. If something feels off, speak up. You know your baby better than any chart.

Below, you’ll find real advice from UK parents and professionals on what to expect, when to worry, and how to support healthy growth without the overwhelm. Whether you’re wondering about feeding frequency, reflux, or whether your baby’s weight gain is slow, there’s something here that’ll help.