If i help my son with his start up business by adding to my quick books will i have to pay two subscriptions?

Hi @g-tucker789 , yes you will pay per subscription. You could add your son company in one account. Please check this and may be you'll need those link :

https://quickbooks.grsm.io/US 

https://quickbooks.grsm.io/us-promo 

Comment back, cheers.

Good question, g-tucker789.

One company file is equal to one QuickBooks Online (QBO) subscription. So if you add another business/company under the same account, you'll need to have another subscription.

Here's how to add a new company:

1. Go to the QuickBooks pricing page and select the subscription you want.
2. Then, you’ll see one of two sign-in pages:
   • If you recently signed in to QuickBooks, you’ll see a page asking you to confirm the account you want to sign in under. If it’s the account you want to manage the new company with, select “Yes, that’s correct.”
   • If you haven’t signed in recently,  you’ll see a page that asks you to create an Intuit account to buy QuickBooks. Scroll all the way to the bottom and look for the small text that says “Adding a company to an existing account?” Select Sign in next to this. When asked, enter the same ID and password you already use for QuickBooks.
     
3. Fill out all the information about your new company and you’re done.

Know more about the process of adding new company into your QBO account through this article: Create or add another company.

Feel free to check out this article to learn more about the available products in QuickBooks: Pricing and subscription levels for QuickBooks Online.

Be sure to get back to me if you have additional questions. It would be my pleasure to help. Have a good one!