Year by year is an expression we often use to refer to a process or event that happens gradually over time. However, there are plenty of other synonyms that can be used to convey a similar meaning. For instance, the phrase annually is often used to describe events that happen once a year, while the term incrementally refers to gradual changes that happen slowly over time. Other alternatives include the phrases step by step, bit by bit, and gradually, all of which can be used to describe a process that happens gradually over a period of time. Depending on the context, these synonyms can be used interchangeably to convey the same meaning as year by year.