Speech sound guide · /θ/ as in “thumb”
My child says “f” for the TH sound
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The short answer
TH is the last English sound most children learn. In a large review of US studies, 90% of children said the voiceless TH (as in thumb) correctly by about 6 years 5 months, and the voiced TH (as in this) by about 5 years 9 months. Saying “fumb” for thumb before then is common.
Most children say it by about 6½ (90% by 6 years 5 months)
How the TH sound is made
TH is made with the tongue tip lightly between the teeth (or just behind them) while air flows out. It’s one of the few sounds children can see, which helps with practice in a mirror.
Common ways children say it differently
- Uses F instead of TH
- “fumb” for thumb, “free” for three.
- Uses T or D instead of TH
- “tumb” for thumb, “dis” for this.
What the age means, and what it doesn’t
“90% by 6 years 5 months” means that in the pooled studies, nine in ten children said TH correctly by that age. About one in ten children who are developing typically get there later, so it’s a guide for when to ask, not a deadline. Ages come from US children learning English.
When to ask a speech therapist about TH
- Your child is past about about 6½ and still swaps or distorts TH.
- People outside the family often find your child hard to understand, or your child is frustrated or teased about how they talk.
- You’re worried. You don’t need to wait for a set age to ask.
More signs: Does my child need speech therapy? In the US, you can ask for a free speech evaluation, or find a certified SLP through ASHA ProFind.
TH practice words
At the start
thumb, think, three, thank
In the middle
birthday, bathtub, toothbrush, nothing
At the end
bath, tooth, teeth, mouth
Use the words your child’s SLP picks first. For keeping practice low-pressure, see how to help at home, and for why a sound can work in sessions before it shows up in conversation, see carryover.
Questions parents ask about TH
Is it normal for a 5-year-old to say “f” for TH?
Yes. TH is learned last: in the 2020 review, 90% of children said the voiceless TH correctly by about 6 years 5 months.
Is “f” for TH just an accent?
In some English dialects, such as some London and some African American English varieties, F or V for TH is a normal feature of the dialect, not a speech error. An SLP takes dialect into account.