申請學校的雅思成績有效期是怎麼算的？

取决于具体学校，哪怕是同一个国家也会有区别。

比如悉尼大学规定：

All English tests need to be no more than two years old at the date of course commencement.

而 Monash 大学规定：

The default time limit is three years from the date the English language measure was completed until the course commencement date.