Credit for tax paid to another state does not match actual tax paid

[siger]

I am a full-time resident of New York. In 2019, part of my income came from and was taxed by California. 

I've filled out all forms for both NY & CA in TurboTax, to the point that the NY section properly identifies the wage portion of the NY total that is already taxed by CA. The "Tax Computed on Your California Return" page reports the expected number, which is the amount of tax I paid to California.

However, the next screen ("Credit for Tax Paid to California") reports a lower tax credit to NY. I expected that it would exactly match the amount paid to CA. In this case, the difference is almost 50%.

What reasons could explain these numbers not matching up? 

[siger]

I did the exercise of filling out form IT-112-R (NY) to understand this further. It seems like the tax credit is not based on the amount of tax paid to another state, rather if X% of the taxable NY income was sourced from CA, then NY reduces its own tax by X%.

In this case, tax paid to California is higher than the tax credit because California taxed my wage income higher than NYS does. 

[KarenJ2 · Accepted solution]

You are correct.  The income of CA / NY * NY taxes is calculated  and compared to the CA tax liability.