Washington Aggregate Bonus Pay Calculator

The free aggregate bonus calculator above, powered by Beyond HCM, is designed to help employers estimate withholding in just a few steps. Simply enter the employee’s bonus amount, regular wages, and filing details to get an estimate of federal withholding, payroll taxes, Washington Paid Family & Medical Leave, WA Cares Fund deductions, and the net impact of the bonus portion.

Because Washington does not impose state personal income tax on wages, this estimate does not include Washington state income tax withholding. However, Washington employees may still be subject to state payroll deductions such as Washington Paid Family & Medical Leave and WA Cares Fund.

Below, you can learn more about what an aggregate bonus is, how the aggregate method works, and how it compares with the flat bonus method.

What Is an Aggregate Bonus?

An aggregate bonus is a bonus payment that is combined with an employee’s regular wages for payroll tax withholding purposes. Instead of taxing the bonus on its own, the employer adds it to the employee’s regular paycheck and calculates withholding based on the combined amount. This approach can affect federal withholding because it is based on the total taxable wages processed for that payroll period.

In Washington, the aggregate method does not create Washington state income tax withholding because the state does not impose personal income tax on wages. However, the bonus may still affect federal withholding, FICA taxes, Washington Paid Family & Medical Leave premiums, WA Cares Fund deductions, and the employee’s estimated take-home pay.

What Is the Aggregate Method?

The aggregate method is used when supplemental wages, such as bonuses, are paid together with regular wages in the same paycheck. Under this approach, withholding is calculated on the total combined pay for the payroll period. Federal guidance allows employers to aggregate the bonus with regular wages and compute withholding as though the entire amount were a single payment.

Washington does not impose state personal income tax withholding on wages, so there is no Washington income tax component when a bonus is combined with regular wages.

To determine how much tax is attributable to the bonus, employers generally:

1 – Add the bonus to the employee’s regular wages
2 – Calculate withholding on the combined amount
3 – Calculate withholding on the regular wages alone
4 – Subtract the regular-wage withholding from the combined withholding

The difference represents the withholding attributable to the bonus portion.

How Are Withholdings Calculated?

To calculate withholding under the aggregate method, you treat the employee’s regular wages and bonus as one payment. You first determine the withholding on the combined total using federal tax tables, the percentage method, or payroll withholding assumptions. Then, you determine the withholding on the employee’s regular wages alone. The difference between those two amounts is the amount withheld for the bonus.

In addition to federal income tax withholding, bonus payments are also subject to Social Security and Medicare taxes. For 2026, the Social Security tax rate is 6.2% with a wage base of $184,500. Medicare remains 1.45%, with Additional Medicare tax applying above the usual federal thresholds.

Washington does not impose state personal income tax on wages, so Washington state income tax withholding does not apply to bonus payments. However, Washington Paid Family & Medical Leave premiums and WA Cares Fund deductions may apply depending on the employee’s wages, year-to-date earnings, and payroll settings.

For 2026, Washington Paid Family & Medical Leave uses a total premium rate of 1.13%, with employees responsible for 71.43% of the total premium. Premiums are applied up to the 2026 Social Security wage cap of $184,500. WA Cares Fund is generally funded through an employee payroll deduction of 0.58% of wages and does not use a Social Security wage cap.

Aggregate vs. Flat Bonus Method

The aggregate method and the flat method are both used to withhold federal taxes on supplemental wages, but they work differently.

With the aggregate method, the bonus is combined with regular wages, which may increase the employee’s total taxable wages for that pay period.

With the flat method, the bonus is usually paid separately and taxed at a flat federal withholding rate of 22%. If supplemental wages exceed $1 million, different federal rules may apply to the amount above that threshold, including mandatory withholding at 37% on the excess.

For Washington, separately paid bonuses are generally not subject to Washington state income tax withholding because Washington does not impose state personal income tax on wages. Washington does not have a statewide employee TDI contribution included in this calculator, but Washington Paid Family & Medical Leave and WA Cares Fund deductions may apply.

Example of the Aggregate Method

Imagine your sales director, Jack, exceeds your July sales goals and earns a $4,000 bonus in August. His regular monthly salary is $6,000, and you choose to include the bonus in his regular paycheck rather than issue it separately.

That means Jack’s August gross pay becomes $10,000. Because the bonus is combined with his wages, federal withholding is calculated based on the full $10,000 payment. To determine the federal tax impact of the bonus, you compare the withholding on $10,000 with the withholding on Jack’s usual $6,000 paycheck.

In Washington, this comparison does not include state income tax withholding. However, the bonus may still affect payroll taxes such as Social Security, Medicare, Additional Medicare, Washington Paid Family & Medical Leave, and WA Cares Fund deductions.

Example of the Flat Method

If you instead choose to pay Jack’s $4,000 bonus separately, the payment would generally be subject to the federal flat supplemental withholding rules. His regular wages would still be paid as usual and taxed under the normal withholding rules for his paycheck.

This method is often simpler. Under current federal guidance, the flat federal withholding rate on supplemental wages remains 22%, with special rules applying when supplemental wages paid to the employee during the calendar year exceed $1 million.

For Washington, separately paid bonuses are generally not subject to Washington state income tax withholding. However, federal withholding, FICA taxes, Washington Paid Family & Medical Leave, and WA Cares Fund deductions may still apply.

Why Use a Bonus Calculator?

Both aggregate and flat bonus withholding methods involve additional calculations, especially when federal payroll taxes and state payroll contributions are involved. Using a payroll bonus calculator can help employers estimate withholdings more quickly and reduce the chance of errors.

The Beyond HCM aggregate bonus calculator is designed to give employers a practical estimate they can use as a starting point when processing payroll in Washington, including federal withholding, FICA taxes, Medicare taxes, Additional Medicare tax, Washington Paid Family & Medical Leave, and WA Cares Fund deductions.

Important Disclaimer

This calculator is provided for informational and estimation purposes only and should not be relied upon as tax, legal, or accounting advice. Actual withholding amounts may vary based on employee elections, payroll setup, pre-tax deductions, Form W-4 elections, Washington Paid Family & Medical Leave rules, WA Cares Fund rules, year-to-date wages, and the way the bonus is processed.

If you need help reviewing your payroll calculations or setting up the right process, the Beyond HCM team is here to help.

Estimate only — not legal or tax advice. Need help managing Washington payroll more confideny? Contact Beyond HCM for support.