You asked Why did the tax refund estimate calculator, using the exact information from my W2, estimate a refund that was $800+ more than I’m actually getting?

To determine why the Tax Estimator is different from the actual return, you can view Tax Summaries for each tool to view the differences, line by line.

 

To do this, first go to the Tax Estimator Tool.  With your information entered, click the Up arrow, next to "Estimated Federal Refund."   This will show you total income, total deductions, taxable income, payments, and your estimated refund.

 

Then log into your TurboTax Online Account and go to Tools/Tax Tools/View Tax Summary. (This summary will list the same row Items)

 

If you are using a desktop version of TurboTax, you can view a similar Tax Summary in Forms Mode from the left hand margin forms list.  

 

Compare these two summaries to see what the differences were and why the Refund calculated differently.  

Do not understand how, where and why the difference? 

To further clarify, the actual Fed refund was significantly higher than that calculated by TT!