This tool will help you answer the question: How much can I earn (and save) teaching English in Japan. Because it's creating a monthly budget it'll work fine if you're not a teacher, but you'll need to adjust some fields like bonus and airfare reimbursement to fit your job.
The budget has default answers and numbers filled in, change what you need and press calculate. To find out more about a field (and how it is calculated) click the text for it.
You can share the budget with your own numbers by changing them and then pressing custom URL. You'll get a link to your own custom version of the budget