How to add a year to an Instant in NodaTime?

From NodaTime's documentation I understand why there is no AddYear on a ZonedDateTime or an Instant. I need some way to get to 'this time next year' however (all the times I need are stored/used in UTC). So far, what I've come up with is this:

var start = SystemClock.Instance.GetCurrentInstant().InUtc();
var nextyear = start.Date.PlusYears(1).At(start.TimeOfDay).InUtc().ToInstant();

Is that the right way to do this? Which of all the reasons for not having an AddYear on ZonedDateTime might I run into problems with here?

Solution

If you're only dealing with UTC, and you're only using the ISO (Gregorian) calendar, then what you've got should be okay, although it can be simplified to:

var nextYear = SystemClock.Instance.GetCurrentInstant()
   .InUtc()
   .LocalDateTime
   .PlusYears(1)
   .InUtc()
   .ToInstant();

The reason it's okay to do this for UTC is that UTC doesn't have any transitions - you don't need to worry about "one year from this local date/time" being either ambiguous or skipped.

It's just worth being aware of exactly what you're doing - that you're adding a year to "the current Gregorian date/time in UTC", not adding a year to "the current instant in time", because an instant doesn't have a concept of "a year".