The IRS Instructions and Publications contain various different worksheets that are used to calculate different amounts reported on your tax return. You should keep a copy of any of these worksheets that apply to you and that you complete. They should be kept with your tax return for the applicable year.
Worksheet for the cost of keeping up a home (to determine if you qualify as Head of Household)
Worksheet for determing support (to determine how much of a person's support you provided, to see if you can claim that person as a dependent)
State and Local Income Tax Refund Worksheet (to see if you need to include a refund in your taxable income)
Worksheet for figuring the cost of group-term life insurance to include in income (if you have group-term life insurance coverage of over $50,000 provided by your employer)
Worksheet for Figuring the Limit on Rental Deductions for a Dwelling Unit Used as a Home
Social Security Benefits Worksheet (to determine if any of your benefits are taxable)
Simplified Method Worksheet (to determine the taxable amount of pensions and annuities received)
Qualified Dividends and Capital Gain Tax Worksheet
IRA Deduction Worksheet
Worksheets for figuring your Modified Adjusted Gross Income for traditional IRA and Roth IRA purposes
Student Loan Interest Deduction Worksheet
Tuition and Fees Deduction Worksheet
Self-Employed Health Insurance Deduction Worksheet
Standard Deduction Worksheet for Dependents
Itemized Deductions Worksheet
Schedule D Tax Worksheet
Deduction for Exemptions Worksheet
Worksheet To See if You Should Fill in Form 6251 – Alternative Minimum Tax
Child Tax Credit Worksheet
Earned Income Credit Worksheet
Earned Income Credit Eligibility Checklist
Any other separate calculations you make, that are not IRS schedules that you file with your return but that you prepare in order to determine the amounts you report on your return, shcould also be kept with your copy of your tax return for that year.