The API pricing is listed on the Pricing page before you sign up for a key, and on the Key Settings page after you've signed up for a key. Pricing is listed per month, and the public API does not have a yearly payment option. The price of the API is determined by the Plan you select, giving you different data sets, and the level of traffic you expect will hit your API key. Features of the API data can be combined into one URL to cut down on the number of hits you need to make. For instance you can get the current conditions and forecast at the same time, instead of making 2 different URL hits. You can sign up for the lowest level you think you will need, and move up the levels as demand on your API key increases. Changes to your billing plan happen same day through the API frontend, and you don't need to change your API key when moving up to different traffic levels. You can also lower your level if you find you are over paying for the service given the number of hits against your API key.