Yes, Singapore Airlines KrisFlyer miles are subject to a "hard expiry" policy of 36 months (three years) from the month they were earned. Unlike many other airline programs where any account activity (like earning or spending a single mile) resets the entire balance, KrisFlyer miles expire on a rolling basis regardless of your recent activity. For example, miles earned in February 2023 will expire on February 28, 2026. The only significant exception is for PPS Club and Solitaire PPS Club members, whose miles do not expire as long as they maintain their elite status. For regular members, you can pay a fee (in miles or cash) to extend expiring miles for a one-time period of six months (or 12 months for Elite Silver and Gold members). It is crucial to monitor your "Miles Validity" in your online account, as once miles have expired, they cannot be reactivated, making it essential to "use them or lose them" for flight redemptions or upgrades before the clock runs out.