Nathanael’s name day is April 22, the feast of Nathanael the Apostle.
Churches that follow the Old (Julian) Calendar keep the same feast on May 5 of the civil calendar. See everything commemorated on April 22.
The saint behind the name
Nathanael the Apostle
April 22, Apostle, Ναθαναήλ ο Απόστολος
Nathanael of Cana in Galilee was brought to Jesus by Philip and, hearing that the Lord had seen him under the fig tree, confessed Him as the Son of God. He was among the disciples to whom the risen Christ appeared at the Sea of Tiberias.
Also celebrating on April 22
These names share the feast, many of them other forms of the same name:
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.