A method for monitoring an aircraft engine during flight, which includes the steps of: for at least one characteristic frequency of the operation of the engine, measuring at least one synchronous vibration level value; for at least one module of the engine, estimating an out-of-balance value of the module in accordance with the one or more vibration level values measured and at least one sensitivity coefficient; estimating a balancing margin of the module in accordance with the out-of-balance value of said module and a maximum threshold; (d) estimating a remaining number of flights of the aircraft prior to balancing and/or a quality indicator of a preceding balancing operation in accordance with the one or more estimated balancing margins and data representing past balancing operations of the engine.