see whether you are covered by a retirement plan or not. If covered, the number should be 89000, i.e. if your income ( line 15 or 1040A) is below 89K, all your contribution (up to 5000) is deductible. Above 10900, none of your contribution is deductible. Between 89K-109K, it is the phase-out area. You can follow the 1040A instruction to figure out.
If you are not covered by your employer's plan, the numbers are 157K-177K, similae as above.