Tax withholding depends on the employee's personal situation and ideally should be equal to the annual tax due on the Form 1040. When filling out a Form W-4 an employee calculates the number of Form W-4 allowances to claim based on their expected tax filing situation for the year. No interest is paid on over-withholding, but penalties might be imposed for under-withholding. Alternatively, or in addition, the employee can send quarterly estimated tax payments directly to the IRS (Form 1040-ES). Quarterly estimates may be required if the employee has additional income (e.g. investments or self-employment income) not subject to withholding or insufficiently withheld. Quarterly payments can also be required for a few years as a penalty for under withholding more than a nominal amount. There are specialized versions of the W-4 Form for other types of payment; for example, W-4P for pensions, and the voluntary W-4V for certain government payments such as unemployment compensation.