Multiplying Dates by Months using If Statement

Hi.
I am working on moving our workflow from google sheets to Airtable.
We have clients who have contracts for 12, 18, 24 or 36 months.

We are trying to have a column where we see their anniversary.
I figured out the 12 month, that was easy because everyone is at least 12 months.

It get’s tricky with formatting after 12 months.

What I want to tell it to do is check if the term is greater than 18. If so, then calculate what the 2 year anniversary is (because not everyone has a 2 year anniversary, or a 3 year anniversary)

I tried this and it didn’t work:
IF([Term]>18, DATEADD({First Month}, 24, ‘months’),"-").

Help!