Hi Michael,
This is assuming that you are staying in your primary home and house hacking. I was a little confused on the way you worded your question because it seemed like you were asking how to calculate cashflow if you didn't live in your home and fully rented out your house.
Cashflow=Rental income- expenses
Rental income: how many rooms will you be renting out? How much can you get for it? Check Facebook Marketplace or craigslist (rooms for rent).
Expenses:
1. Mortgage
2. Property Taxes (never heard of property taxes increasing if you convert a house into a house hack. Very weird... property taxes typically increase when there is a tax reassessment (renovations done, ADU was added, etc...) So maybe that's what people meant when they told you your property tax may go up (i.e. adding an ADU to rent out). But if you keep your house as is, then there shouldn't been a property tax hike.
3. lawn care, utilities, parking spot
4. saving up for capex expenses (i.e. 5-8% of rental income depending on the condition of your home)
5. Repairs & Maintenance (5-8% of rental income)
Take a look at the BP rental calculator to see all the potential expenses you may have while house hacking.
Note: if the cashflow comes out negative, you technically aren't "losing", because your tenant is at least partially covering your biggest monthly expense which is housing...