Yes, your contributions to your employer's Retirement Plan are deductible.
If you contributed through Payroll Deductions, this amount will show on your W-2 in Box 12, so you won't need to enter it elsewhere.
TurboTax will tell you if you're eligible for the Saver's Credit for your contribution.
If you contributed on your own with after-tax funds, enter the amount under Deductions & Credits > Retirement Savings Contribution Credit.
Here's more info on Retirement Plans.
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