After a certain point, when I add to my Medical Expense Summary, the amount of my refund starts to go down instead of up. Why?

[TurboTaxBrenda1]

From your total medical expenses, the eligible amount is 3% of your income or the set maximum for the tax year, which ever is less. For example, if your net income is $60,000, the first $1800 of medical expenses won't count toward a credit.  Therefore your refund will only go up a certain amount. 

You will only claim an amount that will be beneficial to you within a 12 month period. Amounts you can claim 
$2,479. 3% of your net income (line 23600 of your tax return)

How do I enter my medical expenses?

Thank you for choosing TurboTax.

[gnortsmra1]

My point isn't that I don't have enough medical expenses to qualify for a deduction (it easily exceeds 3% of my income), my point is that after a certain point, as I continue to add expenses, my refund starts to go down instead of up. Is there an upper limit to the amount you can claim?