If you only have $4500 in liability, that's true. You'll get a refund if you had more in $4500 tax liability, which would be the case for most people.
I.e. you don't have to owe the IRS come tax time to make the credit work.
?? I chose 4500 as an arbitrary figure; it is not a break point.
You have to owe the Treasury 7500 or more (Line 46) to get your full 7500 credit. This is for an entire Tax Year which is the accounting unit for US Income Tax, not some point in time. Estimated taxes have nothing to do with either the 7500 credit calculation or completing Line 61 Total Tax (form 1040). Line 61 is your 'bottom line' for the Tax Year. So I have no idea what your point is.
Best and simplest way to tax plan is just print up some 1040 forms and pencil in as the tax year progresses. Especially when you are planning charitable deductions or taking capital gains; if you overdo these you can 'lose' money to the Treasury.
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