Hi! I use date picker field in custom post type. How to count published posts that have current year set in date field?
Does this post do what you need?
Once you query but what you need, you can then do something like:
$the_query = new WP_Query( $args );
$totalposts = $the_query->found_posts;
echo $totalposts;
Code untested and will need adjusting to fit your field names etc. but should get you underway!