In the State of Washington, the only portion of your vehicle
registration that is tax deductible (on Form 1040 Schedule A) is the
amount shown on your statement for the RTA (Regional Transit Authority)
tax. Only residents of King, Pierce, and Snohomish counties, and who
live within the Sound Transit District, will have any RTA tax. If you do
not pay RTA taxes, then you do not have a tax deductible portion of
vehicle registration fees for Washington vehicles.
For more information on the RTA, you may visit the following government webpage:
In TurboTax, you would want to enter the full amount of your RTA tax (if applicable to you) that is shown on your Washington vehicle registration statement. You won't reduce the RTA amount, nor will you enter any amounts from your Washington vehicle registration statement other than the RTA tax. This is the dollar amount that you should use for the TurboTax data field that asks for your "deductible portion" of the Washington vehicle registration fees.
Finally, it is also important to keep in mind that you (or anyone claiming this deduction) may or may not actually see any net tax benefit from including this item on your tax return. The reason for this is that you must have enough itemized deductions (in total) to exceed the standard deduction available to all taxpayers. Since more than 2 in 3 taxpayers do not, most people end up taking the (more valuable) standard deduction, rather than itemizing deductions. If you input all your data carefully, however, the TurboTax software will make that determination for you.
Thank you for asking this question.
In Washington, a Use Tax is charged to vehicles when they are registered by a new owner (used vehicle purchased directly from previous owner) or a vehicle purchased out of state (i.e. Oregon).
This tax captures the WA sales tax normally charged upon sale by a Washington car dealer. Since the tax is based on the vehicle value, it is deductible.