You can always see how many check credits you have left in your Account Settings—the number of used checks out of the number of total checks for your subscription plan calculated on the number of keywords tracked with the chosen checking frequency.
Example: If you have 30,000 checks in the subscription plan you chose and you are tracking 50 keywords every 6 hours, the counter will show that you have used 1,400 checks out of 30,000 on the 7th day of your subscription cycle.
Also, when creating or editing a project in SerpWatch, you can see how many keywords you have left for tracking within the chosen subscription plan (with the number of reserved out of total checks and the set check frequency).