W4

W4 is a designation used in different contexts, and its meaning depends on the setting. The most widely recognized use is in the United States as Form W-4, the Employee’s Withholding Certificate.

Form W-4 is completed by employees and given to their employer to determine how much federal income tax to withhold from each paycheck. The 2020 revision redesigned the form to improve withholding accuracy and no longer relies on personal allowances. The current form guides the employee through steps that cover personal information, multiple jobs or a working spouse, dependents, and other adjustments, with a final signature to validate the filing. Employers use the information on the W-4, in conjunction with IRS withholding tables, to calculate federal tax withholding. The form is not used to set state withholding, which is handled separately in many states. If a taxpayer’s situation changes, a new W-4 should be submitted to adjust withholding.

In the United Kingdom, W4 refers to a London postcode district within the wider W postcode area. It is used for mail delivery and location identification in West London and helps distinguish local areas for residents, businesses, and services.

Beyond these, the term W4 may appear as a designation in other domains, including product names or internal coding systems, but the two uses described above are by far the most common. The interpretation of W4 is therefore primarily tax-related in the U.S. and geographic in the UK, with context determining its exact meaning.