First Day Spring 2025. To calculate the first day of spring 2025, we need to determine the date of the vernal equinox, which is the day when day and night are equal in length. When is the first day of spring 2025, and what is the spring equinox?

When is the first day of spring 2025, and what is the spring equinox? In the northern hemisphere, the astronomical start of spring, also known as the spring equinox, will occur on thursday, march 20, at 5:01 am edt in 2025.