"From that day on" is a commonly used phrase that indicates a significant change or event took place at a certain point in time. However, there are a variety of synonyms that one can use to convey the same meaning, such as "since then", "henceforth", "from that moment", "starting then", "following that", "thereafter", "beginning at that point", "subsequently", "afterward", and "from that time forward". These synonyms can help to add variety and interest to your writing while effectively conveying the same message. Choose the synonym that fits your context and tone of the text to make your writing more impactful.