After inadvertently committing an interpersonal transgression, an offender might make an effortful apology (e.g. cancelling an important meeting to make an apology as soon as possible). Such costly apologies signal the apologiser's sincere intention to restore the endangered relationship. The present study investigated this costly signalling model of apology across seven countries (Chile, China, Indonesia, Japan, the Netherlands, South Korea and the U.S.). Participants were asked to imagine that a friend had committed an interpersonal transgression against them and had then apologised in either a costly or non-costly fashion. The results showed that costly apologies were perceived to be significantly more sincere than no cost apologies in the all seven countries. We further investigated whether religious beliefs would moderate the effect of costly apologies. Consistent with our prediction and evolutionary hypothesis, costly apologies were perceived to be significantly more sincere than no cost apologies across religious groups (Buddhists, Christians, and Muslims).