I couldn't find any calculator on Minnowbooster, but @smartsteem basically provides a calculator to let you know how much you will earn from a certain amount of delegation. You can check out yourself by visiting https://smartsteem.com/ and select calculate revenue under delegation, but you must read this blockquote first, which is from Smartsteem website.

These values are not absolute and are changing based on STEEM & SBD-Price, available Reward-Fund and other variables.

I hope this might help you.