Baby Teething Calculator

How to Use the Baby Teething Calculator

To use the calculator, enter your baby's birth date and, if they were born before their due date, the number of weeks premature — then tap the button. The hero result is the next tooth group due, shown as a calendar date window; below it you get how many of the 20 baby teeth are typically in by now, plus the full timeline of all seven tooth groups as dates.

1. Enter the birth date — the exact day your baby was born. Every window counts forward from this date in whole calendar months.
2. Enter weeks premature, if any — leave it at 0 for a full-term baby. For a baby born early, enter how many weeks before the due date they arrived; the timeline shifts later by that many weeks, because teething follows adjusted age.
3. Read the next tooth first. The hero result names the group due next (or the group erupting right now) and its date window. A window is a range, not a deadline — a tooth is normal anywhere inside it.
4. Check the count, then the timeline. “Teeth expected by now” counts only groups whose windows have fully passed, so it stays conservative. The full timeline lists all seven groups so you can plan ahead — for example, knowing the first molars land around 13–19 months, when chewing and brushing change.

Teething rarely arrives alone: it overlaps with the milestones, sleep changes, and feeding shifts of the same months. Parents tracking the bigger picture often pair this timeline with the baby milestones by month calculator, which dates first smiles, rolling, sitting, and first steps from the same birth date.

The same birth date drives several other baby timelines on this site. The baby milestones by month calculator maps developmental milestones to calendar dates, the baby vaccine schedule calculator dates each immunisation visit, and the baby sleep by age calculator shows how total sleep and nap splits change as your baby grows — useful because teething nights often look like sleep regressions, and the two need different responses.

How the Baby Teething Calculation Works

The calculation works by adding each tooth group's eruption window, in whole calendar months, to your baby's birth date — shifted forward by the weeks premature, if any. A baby born on 15 January 2026 has lower central incisors due 15 July to 15 November 2026 (6–10 months later); a baby born 4 weeks early has the same window shifted 4 weeks later, to 12 August to 12 December 2026. The calculator then compares today with each window to find the tooth due next and to count the teeth already expected.

The key facts behind the calculation, each stated as an entity, attribute, and value:

• Lower central incisors — eruption window — 6–10 months (ADA, 2024).
• Upper central incisors — eruption window — 8–12 months (ADA, 2024).
• Upper lateral incisors — eruption window — 9–13 months (ADA, 2024).
• Lower lateral incisors — eruption window — 10–16 months (ADA, 2024).
• First molars — eruption window — 13–19 months (ADA, 2024).
• Canines (cuspids) — eruption window — 16–23 months (ADA, 2024).
• Second molars — eruption window — 23–33 months (ADA, 2024).
• Full primary dentition — total baby teeth — 20 teeth (10 upper, 10 lower).
• First tooth check-in threshold — no tooth by — about 13 months, when a dentist visit is worth booking (AAPD guidance).
• First dental visit — recommended by — the first birthday, or within 6 months of the first tooth (AAPD).
• Adjusted age — definition — chronological age minus weeks premature, used for premature babies until about age 2.
• Teething fever — true fever threshold — over 100.4°F (38°C) is not caused by teething (AAP guidance).
• Permanent teeth — replacement begins at — around age 6, when baby teeth start to fall out.

The full eruption chart

The table below is the ADA (2024) eruption chart in full. Notice how the windows overlap: at 10 months a baby can legitimately be cutting lower incisors, upper incisors, or lateral incisors all at once, which is why “how many teeth” varies so much between babies of the same age.

The insight most teething guides miss: order varies more than timing

Most teething articles present the eruption order as a fixed sequence, and parents worry when their baby breaks it. The data say otherwise: the windows are fairly stable, but the order within overlapping windows is not. Upper lateral incisors (9–13 months) can precede upper central incisors (8–12 months) in a healthy baby, and a canine can beat a first molar to the surface, because their windows overlap by months. What actually deserves attention is a window closing with no tooth at all — no first tooth by about 13 months, or no molars by 20 months — not a swapped order inside an open window. That distinction is why this calculator reports windows and counts, never a single “your baby should have X teeth” verdict: the count it shows is the conservative floor (groups fully passed), not a pass-or-fail target.

Teething also changes what goes in the mouth, which is why it overlaps with feeding questions. When the first molars arrive around 13–19 months, chewing capacity jumps and many babies move toward more textured foods; the breast milk intake calculator helps track how milk needs shift as solids take over, and the baby wake window calculator helps separate a teething night — pain that eases with a cold teether — from a wake window that has simply grown too short.

Worked Example: Baby Teething

Take a baby born on 15 January 2026, full term (0 weeks premature). The calculator adds each group's window in whole calendar months to 15 January 2026: lower central incisors 15 July to 15 November 2026 (6–10 months), upper central incisors 15 September 2026 to 15 January 2027 (8–12 months), upper lateral incisors 15 October 2026 to 15 February 2027 (9–13 months), lower lateral incisors 15 November 2026 to 15 May 2027 (10–16 months), first molars 15 February to 15 August 2027 (13–19 months), canines 15 May to 15 December 2027 (16–23 months), and second molars 15 December 2027 to 15 October 2028 (23–33 months).

On 26 October 2026, that baby is about 9 months old and sits inside the lower central incisor window (15 July–15 November 2026) — so the hero result reads “Lower central incisors: Jul 15, 2026 – Nov 15, 2026,” and the count reads “0 of 20 baby teeth typically in by now, plus lower central incisors erupting now,” because no group's window has fully passed yet. If the same baby had been born 4 weeks premature, every date shifts 4 weeks later: the lower central incisors would be due 12 August to 12 December 2026, and on 26 October the baby's adjusted age would be about 8 months — still inside the window, but with more of it ahead than behind.

How Accurate Is the Baby Teething Calculator?

The calculator is accurate as a date translation of the ADA (2024) eruption chart, not as a prediction of the day a tooth will appear. Its arithmetic is exact — adding 6 and 10 calendar months to 15 January 2026 gives 15 July and 15 November 2026 with no rounding — but biology is not: a tooth can arrive anywhere inside its window, and windows themselves are population ranges that cover most, not all, babies. Roughly speaking, the chart's windows capture the middle of the distribution; babies outside them are usually still healthy, just early or late.

Three limits deserve honesty. First, calendar months are not exactly equal — the calculator counts whole months, so a baby born on 31 January gets a window starting 31 July or 30 June depending on the month's length; the clamp to the month's last day keeps dates valid but shifts them by a day or two. Second, adjusted age is an approximation: it assumes teething tracks the due date exactly, which holds well in the first two years but is not a precise biological law, and most clinicians stop adjusting after age 2. Third, the calculator cannot see the mouth — gum swelling, a visible white ridge, or a tooth that has partially erupted all mean more than any date, and a tooth that looks discoloured, pitted, or oddly shaped is worth a dentist's look regardless of timing. Within those limits, a window-based timeline beats any single “first tooth at 6 months” slogan, because it tells you both when to expect a tooth and when to stop expecting it quietly.

If your baby's nights are the problem rather than the dates, the baby sleep by age calculator shows whether total sleep is actually off for their age, and the diaper cost calculator covers the other fast-moving number of the same months — how many diapers the teething, drooling, occasionally looser-stooled phase really uses.

The Bottom Line on Baby Teething

The bottom line is simple: most babies get their first tooth — a lower central incisor — between 6 and 10 months (ADA, 2024), collect all 20 baby teeth by about 33 months, and vary far more in the order of teeth than in the timing. Enter the birth date, adjust for prematurity if needed, and read windows, not deadlines: a tooth anywhere inside its window is on schedule, and the only dates that deserve a call are a first tooth missing past about 13 months or a first dental visit delayed past the first birthday. Updated 2026.