The most common question parents ask about potty training is when to start. The most useful answer isn't a number, it's a set of readiness signals that show up somewhere between about 18 months and 3.5 years, in no particular order, and that are much more predictive of a smooth experience than the child's age is.

Here's what to look for, what to make of mixed signals, and what to do if readiness feels like it isn't coming.

The three kinds of readiness

Potty-training readiness has three overlapping components. All three usually need to be in place before training goes well. Starting when only one is present is one of the top reasons training gets stuck.

Physical readiness

Staying dry for 2+ hours at a stretch. This is bladder-control biology. Without it, they physically cannot hold long enough to make it to the toilet.
Predictable bowel timing. Bowel movements happening at roughly the same times of day, most days.
Recognizing wet or soiled diapers. Discomfort in a wet diaper, wanting to be changed promptly, pulling at their diaper, all signs that awareness of the wet-vs-dry sensation is coming online.
Being able to pull pants up and down. Loose-fitting bottoms with elastic waists count.
Being able to sit on a small toilet or potty for a few minutes. Balance and core control need to be strong enough.

Cognitive readiness

Following simple two-step instructions. "Go to the bathroom and sit on the toilet" is a two-step instruction.
Understanding basic body vocabulary. The words you use for peeing and pooping, whatever they are, need to actually mean something to the child.
Imitating adult routines. Wanting to do what parents and older siblings do is a strong cognitive readiness signal.

Emotional readiness

Showing interest in the toilet. Watching, asking, wanting to see.
Wanting to be more grown-up. Some kids proudly identify with being "a big kid" and lean into it.
Not being in a stressful transition. New baby, move, starting daycare, hospital stay, these are windows when starting training is likely to go worse. Wait a few weeks after big changes.

Not all three components arrive at the same time. Most kids have physical readiness first, cognitive readiness a few months later, and emotional readiness sometimes lagging further.

Signs that suggest waiting

Some signals mean it's not time yet. Common ones:

Actively hiding to poop. This is not readiness, this is early-stage privacy-awareness, which is different. Hiding often means the child is more comfortable in a familiar routine (diaper) than they will be in a new one.
Fighting diaper changes. Sometimes read as "wants out of diapers," this can just be a phase of resistance to being interrupted. It doesn't mean they're ready for training.
Regression from any prior progress. If they had been using the potty a few weeks ago and stopped, don't force it. That's a signal to pause and let it come back naturally.
Constipation. If bowel movements are hard, infrequent, or painful, address the constipation first. Training on top of constipation is where a lot of encopresis stories start. Our Childhood Constipation guide walks through the basics.
Chronic breath-holding, tantrums, or heightened anxiety. These usually mean this isn't the emotional window.

What to do while waiting

If your child isn't ready but you're impatient, the best thing you can do is not start yet. Starting before readiness is one of the top causes of long, tense training arcs.

While you wait:

Let them come with you to the bathroom sometimes. Narrate what you're doing in a matter-of-fact tone.
Read simple books about using the toilet. Some kids get interested.
Have a small potty around. Don't push it. Just let it exist.
Model what dry underwear feels like, put a spare pair somewhere they can see.
Keep the language low-pressure. "Sometime, when you're ready, we'll try. There's no rush."

When they're ready, you'll usually get a clear tell, often an unprompted request, or several days of being visibly interested, or a stretch of dry diapers that surprises you.

What if readiness signals are mixed

Very common. Physical readiness at 22 months, cognitive readiness at 28, emotional readiness at 30. You don't have to wait for all three at 100% before starting, but starting with only one out of three is the setup for the most frustration.

A rough guideline:

All three showing: start
Two of three showing consistently: probably start, prepared to slow down if it goes badly
One of three showing: not yet

Slowing down mid-training is not failure. It's just recalibration. Kids don't develop in straight lines.

What if readiness never seems to come cleanly

Some kids never give a big, obvious "I'm ready" signal. They just kind of drift toward using the toilet gradually over months. This is fine. Late-and-drifting can be a longer arc, but it's often a lower-tension one.

If your child is past 3.5 and none of the signals seem to be arriving, it's worth talking to your pediatrician, mostly to rule out constipation, sensory sensitivities, or developmental factors that might be shaping the pattern.

If constipation is part of the picture (very common), starting potty training on top of it will make everything harder. Treat the constipation first, then revisit training a few weeks later. Our Managing Constipation Without a Power Struggle post walks through the general shape of that.

The calmer starting posture

However and whenever you start, the most useful posture is: this is a skill they will get. Not this month. Not necessarily this year. But they will get it, and pressure from you now is more likely to lengthen the arc than shorten it.

For the broader approach to a low-pressure toilet routine, our Potty Training Help guide is the reference. And once training gets to the daily sit-routine stage, Quiet Sit is what we built for running that routine every day without turning it into a source of conflict.