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Tax planning for high earners with a salary and side income

By Claud Cornetti, CPA · Licensed in New Jersey and New York

Updated 19 October 2026

Why do I owe money when tax is withheld from my pay?

Your employer withholds based on your wages and W-4. Nobody withholds on consulting income, rental profit or capital gains, and bonuses and stock compensation are often withheld at a flat rate that can be lower than your actual bracket.

The IRS expects tax to be paid during the year. You avoid the underpayment penalty if you owe less than $1,000 after withholding. You also avoid it if withholding and estimated payments cover the smaller of 90% of your 2026 tax or 100% of your 2025 tax. If your 2025 AGI was over $150,000 ($75,000 married filing separately), that second figure becomes 110%. The 2026 estimated payments are due April 15, June 15 and September 15, 2026 and January 15, 2027.

Withholding is treated as paid evenly through the year, while estimated payments count when you make them. So a larger withholding in November or December can cover an earlier shortfall. New Jersey and New York have their own estimated payments (Form NJ-1040-ES and Form IT-2105) and their own penalty rules.

I live in New Jersey and work in New York. Where do I pay?

New York taxes the wages you earn for work done in New York, and you file a nonresident return (Form IT-203). New Jersey taxes all your income as a resident. It gives you a credit on Schedule NJ-COJ for the New York tax on the same income, up to the New Jersey tax on that income. In effect, you pay the higher of the two states' tax on those wages, not both. New York City's income tax applies only to city residents, so a New Jersey resident doesn't owe it.

Days you work from home need attention. Under New York's convenience of the employer rule, a day you work from your New Jersey home for a New York employer usually counts as a New York day. The exceptions are when your employer requires you to work outside New York, or when your home office meets New York's test for a bona fide employer office. Keep a record of where you work each day.

What changes when my income crosses certain levels?

Several rules start, stop or shrink at specific income levels. For 2026:

• The 3.8% net investment income tax applies to investment income once modified AGI passes $200,000 for single filers or $250,000 for joint filers, amounts that aren't indexed.
• The 0.9% Additional Medicare Tax applies to wages and self-employment income above the same amounts. Employers withhold it only on wages over $200,000 from that employer, so two working spouses can be under-withheld.
• The SALT deduction cap of $40,400 shrinks once modified AGI passes $505,000 and falls to $10,000 at about $606,333.
• The 37% bracket starts at $640,600 for single filers and $768,700 for joint filers, and a new rule limits the benefit of itemized deductions in that bracket.
• Direct Roth IRA contributions phase out between $242,000 and $252,000 of modified AGI on a joint return, and between $153,000 and $168,000 for single filers.
• The child tax credit phases out above $400,000 on a joint return and $200,000 for other filers.

Most of these use modified AGI, so the timing of income and retirement contributions matters.

How is side income taxed?

Freelance or consulting income from a sole proprietorship, including a one-owner LLC, goes on Schedule C. You pay income tax at your regular rate plus self-employment tax on 92.35% of your net earnings, and half of the self-employment tax is deductible. Below $400 of net earnings, there's no self-employment tax.

High earners get a break here. The 12.4% Social Security portion only applies up to the 2026 wage base of $184,500, and your W-2 wages count toward it first. If your salary already exceeds $184,500, your side income pays only the 2.9% Medicare portion, plus the 0.9% Additional Medicare Tax where it applies.

You can deduct ordinary and necessary business expenses, such as equipment, software, business mileage and a home office used regularly and exclusively for the work. If the activity isn't run to make a profit, the IRS can treat it as a hobby, deny the expenses and still tax the income. An LLC alone doesn't change your federal tax. An S corporation election can, but if your salary is already above the Social Security wage base, the payroll tax it saves on side income is smaller, and the costs stay the same. More on entities and S corporations for business owners.

Can I save more for retirement through my side business?

Often, yes, through a solo 401(k) or SEP-IRA on top of your plan at work. The catch is the employee deferral limit. For 2026 it's $24,500, plus an $8,000 catch-up at age 50 or older ($11,250 instead at ages 60 to 63). It's a per-person limit across every plan you're in, so if you max out your 401(k) at work, you've used it. Starting in 2026, if your 2025 Social Security wages from your employer were over $150,000, your catch-up contributions to that employer's plan must be Roth. The employer side of a solo 401(k) is different. Your own business can contribute roughly 20% of your net self-employment earnings, and that plan has its own $72,000 limit for 2026, separate from your employer's plan. A SEP-IRA uses the same roughly 20% math, up to $72,000.

A sole proprietor with no employees can generally set up a solo 401(k) for 2026 as late as April 15, 2027, the return due date without extensions. Once plan assets pass $250,000 at year-end, the plan files Form 5500-EZ each year.

Is the SALT deduction worth it for me?

It depends on your income and what you pay. For 2026, you can deduct up to $40,400 of state and local taxes if you itemize, but the cap shrinks between $505,000 and about $606,333 of modified AGI, down to $10,000. Itemizing only helps when SALT, mortgage interest and charity together beat the $32,200 standard deduction for a joint return. If your side income runs through a partnership or S corporation, New Jersey's BAIT election can move part of the state tax outside the cap. Read our full answer on the 2026 SALT cap.

What to bring to the first call

• Federal and state tax returns for the last two years
• Your latest pay stub, with year-to-date wages and withholding
• 1099s and income records for this year's side income
• Estimated tax payments made this year, federal and state
• Your year-to-date 401(k) contributions and details of any side-business retirement plan
• A record of days worked from home, if your employer is in New York

Questions we hear

Should I raise my withholding instead of making estimated payments?

It can be simpler. Federal withholding counts as paid evenly through the year, so a larger withholding late in the year can cover an earlier shortfall, while estimated payments count only from the day you pay them.

Do I need an LLC for my side business?

Not for federal tax. A one-owner LLC is taxed like a sole proprietorship unless it elects otherwise, so the decision is mainly about legal liability. We look at an S corporation election once the profit can carry payroll and the extra returns.

I work from home two days a week for a New York company. Do I pay New York tax on those days?

Usually yes, under New York's convenience of the employer rule, unless your employer requires you to work from New Jersey or your home office meets New York's test. New Jersey credits the New York tax on that income, within limits.

Can I use a solo 401(k) if I already max out my 401(k) at work?

Not for employee deferrals, because that limit is shared across plans. Your side business can still make employer contributions, within the separate $72,000 limit for its plan.

This page is general information about the rules in effect for 2026. It is not tax advice for your situation, and reading it does not make you a client. See our Terms of Use.