As the other members have told you, the correct form is 'a year'.

This is because the sound represented by the letter 'y' is a consonant (like b,c,d,f,g and so on). We use 'an' before vowel sounds - 'an apple', 'an egg', 'an Indian', 'an orange' or 'an umbrella'.

But.....

Remember that this is a rule about SOUNDS, not spelling. 

In fact, we often use 'an' before words which are written with initial consonants. One important exception to the general rule is the silent 'h'. We say 'an hour' and 'an honour', because the 'h' is not pronounced. These words are written with an initial consonant, but pronounced with a vowel sound.

We also often use 'a' before words which are written with vowels at the beginning. We say 'a university' and 'a European', for example, because these words are pronounced with an initial 'y' sound, the same as 'year'.

The other thing to remember is that the "names" of consonants often start with vowel sounds. So we say, for example, 'My name begins with an S', because 'S' is pronounced as 'ess'.

I hope that all makes sense.

All good stuff above, just remember not to get focused on the noun if you start adding adjectives.

For example, you have to switch to 'an' if you want to say "I had an incredible year!" 

Correct is "a year"

Here is the general rule:

"an" comes before words beginning in a, e, I, o, and u

"a" comes before all other words