Standar deduction

If you choose new regime you are exempted from Standard deduction of existing regime.

If you choose to file return under new tax regime, then you will not get standard deduction of Rs. 50,000/- from salary income

Some other deduction which u can't claim under new tax regime :
Standard deduction: Rs 50,000
House rent allowance: Depends on salary structure and rent paid
Housing loan interest: Rs 3.5 lakh for affordable housing, Rs 2 lakh for others
Investments under Sec 80C: Rs 1.5 lakh
Leave travel allowance: Tax free if claimed once in block of two years
NPS contribution: Rs 50,000
Medical insurance premium: Rs 25,000 (Rs 50,000 for parents and senior citizens)
Savings bank interest: Rs 10,000 under Sec 80TTA
Interest income (for senior citizens): Rs 50,000 under Sec 80TTB
Education loan interest: Interest paid for eight consecutive years
Disability of self or dependant: Rs 75,000 to Rs 1.25 lakh depending on disability
Treatment of self or dependant for specified disease: Rs 40,000 (Rs 1 lakh for senior citizens)
Donations to specified entities: 50-100% of the amount donated