Including Mortgage Principle in Budget

See:

https://quickbooks.intuit.com/learn-support/en-us/chart-of-accounts/set-up-a-mortgage/00/202617

I don't think you can include it in the budget per se but you should be able to use the lenders amortization schedule and/or Banking > Loan Manager, to estimate the amount of interest and principal to be paid for a certain period.

You can set up a long-term liability account to track your mortgage, @jbooze1. 

First, set up the loan account:

1. Go to the Accounting tab, then click the New button.
2. Set the Account Type to as Long Term Liabilities and the Detail Type to Loan Payable.
3. Enter the name of the account, then click Save and close.

Then proceed in recording an opening balance for the loan:

1. Click the Plus (+) icon, then select Bank Deposit.
2. Select the bank account where the loan funds will be deposited.
3. Type in the date of this deposit.
4. Enter the loan payable account with the amount under the Account column.

Lastly, here's how you can record a loan payment:

1. Click the Plus (+) icon, then select Check.
2. In the Category Details section, enter the following information.
3. First line: Liability account for the loan and the amount of payment.
4. Second line: Expense account for the interest and the amount.
5. Succeeding lines: Any additional fees along with the appropriate accounts.
6. Select Save and close.

See this article for detailed guidance: Set up a loan in QuickBooks Online.

For any other questions, drop them in the comments below. I'd be glad to answer them for you.