O, evde olmalı.
English: He/she must be at home.
In Turkish, 'tahmin ve olasılık bildiren yapılar' are grammar structures used to express guesses, assumptions, or probability about something that is not certain.
Use these forms in Turkish when you want to guess, assume, or talk about something that is probably true but you are not completely sure. They are common when talking about the present, past, or future with uncertainty.
O, evde olmalı.
English: He/she must be at home.
Ali gelmiş olmalı.
English: Ali must have arrived.
Saat ondur.
English: It is probably ten o'clock.
Dışarıda yağmur yağıyor olmalı.
English: It is probably raining outside.
O, bu haberi duymuş olsa gerek.
English: He/she must have heard this news.