How can I split an existing bill to multiple projects? When I try, the entire bill shows as cost against each project i.e. 10k bill w/2k cost on 5 projects.

Welcome to the Community forum, amy-yachtsalesin.

You can assign a customer/project per line item on your bill transaction. Here's how:

1. In the left menu, click the + New button. 
2. Choose Bill.
3. Select the vendors name in the Vendor field.
4. Under Category details or Item details, enter the details like cost and account, then choose a specific Customer/Project.
5. Tap Save and close. 

Once done, the amount designated to each project will show on the Overview tab on your Project page. 

For more information about projects, see below articles:

• Projects FAQs
• Set up and create projects in QuickBooks Online

If you have any additional questions or concerns about QuickBooks, please reach out to me. Have a great day.

I am having a similar problem and it seems like Quickbooks needs to update the process.  I am doing bookkeeping  for a firm and have assigned projects to specific clients.  The firm is renting space, and when the firm receives a bill for rent each month, there is also a charge for copies that were made by the firm.  The copies are chargeable to projects.  When entering the check for payment of the rent and copies, I split the payment into a Rent/Lease Expense and a Client-Related expense.  I assign the appropriate project to the client-related expense, but when I run the project report, the entire amount of the check is charged to the client's project.  I would like for QB to make it so that only the amount for the copies gets charged to the project.  As it stands now, QBO  is creating inaccurate project cost tracking until this is fixed.

This needs a fix after 2 years. Pivoting to another platform for a number of our clients is looking like more of a possibility as this is a MUST for job costing. The "work around" suggested is not a feasible solution for a modern company. Please escalate the priority on this.