# thirties

/ˈθɝtiz/ (US) · /θˈɜːtɪz/ (UK) · CEFR B1 · Noun

Source: https://englishreference.com/word/thirties
Updated: 2026-05-07

## Definition

the years between 30 and 39 in a person's life or in a century.

For teachers: the period of time between the ages of 30 and 39 inclusive, or the years from 30 to 39 within a specific century.

## Examples

- She decided to change her career in her early thirties.
- Many people find that they become more confident in their thirties as they gain professional experience.
- The global economy underwent significant shifts during the nineteen-thirties, a decade marked by both deep financial depression and the rapid development of industrial infrastructure.

## Pitfalls

- Not "He is in his thirty's" but "He is in his thirties" — Do not use an apostrophe to make a decade or age group plural.

## Usage notes

- Always used in the plural form; typically preceded by a possessive adjective or 'the'.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.