Domain names are cheap and abandonment is infrequent and unlikely to save much money, for most people on HN. So renew them early, for long terms. For your business or blog or other domain which will be a going concern for the foreseeable future, go renew it for ten years. If your business gets sold to Amazon tomorrow, oh well, that cost you only $60 ~ $80 or so.
I own a small stable of domains (a few dozen) and keep most of them on rolling two year registrations, with my main ones (product sites, my blog, etc) on rolling five year registrations. I renew all of them yearly. This way, screwups by myself, my bank, Paypal, or GoDaddy probably won't deprive me of use of my property.