I have a mortgage starting in August, and would like to see how it affects my budget. Wouldn't income need to be shown for me to do this?
Here is how you would handle this in YNAB.
You start YNAB in June.
You create categories for the expenses you expect to have and savings you want to keep.
You account for all your money and give all of it a job by assigning it to the categories you created.
You get paid in June and allocate all the dollars you get to jobs.
---Build balance in categories that occur less frequently (insurance, property taxes, car replacement)
You get paid in July and because your buffered you don't need any of that money in July, so you send it to August.
You allocate a portion to your mortgage and dole the rest out to other Jobs/Categories
You may find you have to dole less to some categories if the mortgage expense is higher than say your rent expense used to be.
Now you say - but I really want to forecast it Budget_Ninja.
Ok, ok. But I strongly suggest you don't do it in your working copy of YNAB.
Create a second copy and forecast your heart out. There are several threads on how to accomplish this but a quick way would be to add the expected income to a 'Unearned Income' Account which is On Budget instead of leaving it in the schedule.