To the day
Definition 1 of 2
Pro Tip 1/3Past Events
Use 'to the day' when referencing a significant event's exact anniversary. 
It's been ten years to the day since they first met.
Pro Tip 2/3Emphasizing Precision
'To the day' adds emphasis to the exactness of the time that has passed. 
He returned fifty years to the day after leaving his hometown.
Pro Tip 3/3Memorable Dates
Often used for dates that are easy to remember or hold personal value. 
She passed her driving test one year to the day after her brother did.