Nagano to Narita same day

How early do you recommend getting to Narita for an International flight? I was planning to leave from Nagano in the morning and my flight isn't until 18:05. So I should have plenty of time to make it, but wondering how early I need to leave.

Most international flights require you to be there 3 hours ahead of take off. Look at your booking confirmation.

So aim for that and use whatever transit website (eg hyperdia) to calculate when you need to depart Nagano.

Look like you might get a few hours somewhere between Nagano and Narita as you wont be in transit all day.

Two hours rather than three would be my expectation for a sensible time before a flight departure. (Check-in counters don't open until three hours before for most of the flights I take.)
Nagano to Narita is about three hours so there are several options departing around 12:30 that get you there by 4 p.m.

Thank you.

I'll probably leave mid morning and take in a few sights and lunch around Tokyo Station before heading to airport.