Working per diem, PRN, or two nursing jobs? Your W-4 at each job doesn't know about the others. Find out how much extra to withhold — before you get surprised in April.
Taxable wages only — exclude non-taxable housing & meal stipends.
I've been working some form of per diem or PRN shifts since my second year of nursing. And I'll be honest — the first time I filed taxes with two jobs on my W-2, I owed $2,800. Not because I did anything wrong. Because the W-4 system wasn't designed for nurses who work multiple income streams.
Here's the fundamental problem: each employer withholds federal income tax as if that job were your only income. Your primary hospital withholds assuming the standard deduction applies once. Your per diem agency does the same — applying the full standard deduction again. But you only get one standard deduction on your actual tax return. That double-counted deduction is why nurses with two jobs consistently owe at filing time.
Federal income tax uses progressive brackets — the more you make, the higher the rate on the portion above each threshold. When you have two jobs:
The second job's withholding came up short by roughly the difference between those two rates. On $20,000 of per diem income, that gap is around $2,000 in under-withheld federal tax — not counting any state income tax exposure.
Travel nurses and per diem workers often receive a package that mixes taxable wages with non-taxable stipends. Understanding which is which is critical for accurate withholding estimates:
| Payment Type | Taxable? | Notes |
|---|---|---|
| Hourly / base wages | Yes | Always subject to federal, FICA, and state income tax |
| Housing stipend (travel) | No* | Non-taxable only if you maintain a tax home and duplicate expenses |
| Meals & incidentals (M&IE) | No* | Non-taxable up to GSA per diem rate for the location |
| Per diem / PRN shift pay | Yes | The hourly rate for the shift — fully taxable |
| Sign-on / completion bonus | Yes | Taxed as supplemental wages (flat 22% federal withholding) |
* Stipend non-taxability requires maintaining a legitimate tax home. If the IRS determines you have no permanent home, all stipends become taxable income.
When you enter income into this calculator, only include the taxable portion — your actual wages and any taxable bonuses. Do not include housing or M&IE stipends unless your tax home status is in question.
The cleanest solution: submit a new W-4 to your primary employer and fill in "Additional amount, if any, you want withheld from each paycheck" on Step 4c. This extra withholding comes out of every paycheck automatically and covers your per diem income tax exposure.
The calculator above estimates this number. The math: take your projected annual underpayment and divide by the number of paychecks remaining in the year (or by your full pay period count if you're planning ahead for next year).
Example: Bedside RN + Per Diem PRN
Sarah earns $78,000/year at her hospital job (biweekly pay, single filer). She picks up $24,000/year in per diem PRN shifts. Combined: $102,000 → top marginal rate 22%. Her per diem agency withholds as if she earns $24K alone (12% bracket). Gap: roughly $2,400/year. Solution: add $93/paycheck extra on her hospital W-4. Total tax stress: zero come April.
The IRS charges an underpayment penalty when you owe more than $1,000 at filing AND your withholding is below either:
In 2026, the underpayment penalty rate is approximately 8% annually on the shortfall. For a nurse with a $2,000 gap who owes for 6 months, that's roughly $80 in penalties — small but avoidable. This calculator flags when your gap crosses the penalty threshold.
Yes — if you're a W-2 employee of the agency (most per diem nurses are), they must withhold federal income tax, Social Security, and Medicare. If you're a 1099 independent contractor, no withholding occurs and you're responsible for quarterly estimated tax payments. This calculator is for W-2 employees only.
The old allowance system was eliminated in 2020. Today's W-4 uses dollar amounts in Step 4. To increase withholding, add an extra dollar amount in Step 4c ("Extra withholding") rather than adjusting allowances. Claiming "Exempt" is different — it stops all withholding and is only valid if you owed $0 last year and expect to owe $0 this year.
Either works, but adjusting your W-4 at the primary job is simpler for most nurses — it's automatic and avoids the quarterly due-date hassle. Estimated payments (Form 1040-ES) make more sense if your per diem income is inconsistent or you're a 1099 contractor. Due dates: April 15, June 15, September 15, January 15.
Yes — but only if you meet IRS requirements: you must maintain a permanent tax home that you return to between assignments, and you must incur duplicate housing expenses during travel. Nurses who sold their home, live only in travel housing, or whose "tax home" is the travel location are not eligible. IRS audits of travel nurse stipends increased significantly after 2022. If your tax home status is unclear, consult a tax professional who specializes in travel nursing before counting those stipends as non-taxable.
Some agencies "gross up" certain payments or include the employer's share of health insurance in your taxable wages, or convert non-cash benefits. Review Box 1 (federal wages) vs. Box 3 (SS wages) on your W-2 — they're often different. For this calculator, use Box 1 as your taxable wage figure for the second job.
Jayson Minagawa, BSN, RN
Unit Manager & MDS Coordinator · 12+ Years RN
I built this calculator after years of picking up per diem shifts and getting surprised at tax time. The W-4 system was designed for single-income earners. If you work multiple nursing jobs, you have to actively manage your withholding or you will owe in April.
Disclaimer: This calculator provides estimates for educational purposes only. Federal tax law is complex and individual circumstances vary widely. Consult a qualified tax professional for advice specific to your situation. Tax rates and brackets shown are estimates for 2026 and may not reflect final IRS guidance.