Every December, somewhere between the holiday party and the last workday of the year, your final pay stub of the year shows up. Most people glance at the net pay, confirm it looks normal, and move on.
That's a mistake. The December stub is the single most important pay stub of the year, because it's your last chance to catch problems before they become W-2 errors, which become tax return errors, which become IRS notices six months later.
A proper year-end review takes about twenty minutes and can save you weeks of headache. Here's exactly what to check.
Why the December stub matters
Your W-2 is built from your year's pay stub data. If something's wrong on your stubs throughout the year, it'll be wrong on your W-2 too. Once the W-2 is issued (usually late January), correcting it requires a W-2c — a corrected W-2 that your employer has to file separately. It's not the end of the world, but it delays your tax return and it's a hassle.
The December stub is when you can still catch problems cheaply. Your YTD totals should match what you're expecting. Your deductions should reflect the year's actual elections. Your benefits should be consistent with what you enrolled in. If anything's off, you have one last payroll cycle to flag it before the W-2 goes final.
Most people don't do this check. I didn't for years, and I got bitten once by a missing 401(k) match that was never reflected in my records, which took months to untangle. I'd rather spend twenty minutes in December than twenty hours chasing a correction in April.
The checklist
Here's what to actually look at, in order.
1. YTD gross earnings. Does your December YTD gross match roughly what you were expecting for the year? If your salary is $80,000 and your YTD gross is $82,000, that difference is explained by overtime, bonuses, or other extras — make sure it reconciles. If your YTD gross is $78,000 when you were expecting $80,000, something's missing. Dig in.
2. All expected earnings categories. If you earned overtime, bonuses, commissions, or tips during the year, are they all reflected? Bonuses are especially worth double-checking, because they sometimes get paid through different systems or delayed, and a bonus that "didn't make it onto this stub" might not have been processed correctly.
3. YTD federal tax withheld. Compare your YTD federal tax to your expected annual tax liability. If you've withheld significantly less than you'll owe, you might face underpayment penalties — and you have a few days left in the year to make an estimated tax payment to avoid that. If you've withheld significantly more, you're getting a big refund, which means you gave the IRS an interest-free loan and should probably adjust your W-4 for next year.
4. YTD Social Security tax. Should be 6.2% of your gross earnings up to the annual Social Security wage base. If you earned above the wage base, your YTD Social Security should have stopped growing partway through the year. If it kept growing past the wage base, something's wrong.
5. YTD Medicare tax. Should be 1.45% of your full gross. No cap. Double-check this is right — unlike Social Security, Medicare doesn't stop at a wage base.
6. YTD 401(k) contributions. If you're trying to max out your 401(k), are you on track? Annual limits change yearly, so check the current-year limit. If you're behind and want to hit the max, you might still have one more pay period where you can increase your contribution percentage. If you're at the cap exactly, great. If you're over the cap, that's actually a problem — excess contributions need to be withdrawn before April 15 or they create a tax mess.
7. Health insurance deductions YTD. Multiply your monthly premium by 12 (or your biweekly premium by 26) and compare to YTD. They should match, adjusted for any mid-year rate changes or enrollment changes. If they don't, you might have been over- or under-charged.
8. Other pre-tax deductions YTD. HSA contributions, FSA contributions, commuter benefits, dental, vision — each should reflect your actual elections for the year. HSA is especially worth checking, because if you've under-contributed relative to your target, you can still make catch-up contributions outside of payroll (directly to the HSA from your bank) before the tax deadline.
9. Post-tax deductions YTD. Roth 401(k), supplemental life insurance, garnishments, union dues. Same idea — the YTD should match your expected annual total.
10. Net pay total. Sum your actual net pay for the year (if your stub shows a YTD net) and compare to your bank deposits for the year. If they don't match within a few dollars, you have a reconciliation problem to investigate.
Red flags to watch for
Some patterns are signs of specific problems.
Missing retroactive adjustments. If you got a raise mid-year that included retroactive back-pay, make sure the retroactive amount shows up in YTD earnings. I've seen retro pay get paid but never reflected in YTD totals — which means the W-2 will understate your earnings.
Bonus taxation anomalies. If your employer paid a bonus during the year, the federal tax withholding on that bonus is probably calculated at a flat supplemental rate (often 22%). Check that the bonus payroll period's stub shows the correct withholding pattern.
Benefits changes that didn't propagate. If you changed your 401(k) contribution percentage in July, your pre-July stubs should reflect the old rate and your post-July stubs the new rate. If the change never took effect, your YTD 401(k) will be lower than expected.
Phantom deductions. Occasionally, a deduction persists after you canceled it. If you dropped your dental coverage in March but the dental deduction kept coming out of your paycheck, your YTD dental deduction will be higher than it should be — and you might be owed a refund.
Double-counted bonuses. The opposite problem: sometimes a bonus gets processed twice, or through two separate payroll systems, and you end up with double the expected bonus amount in YTD. This is a much nicer problem to have, but it'll cause tax confusion if not corrected before the W-2.
What to do if you find a problem
Start with payroll or HR immediately. December is busy for payroll departments — they're processing year-end — so flagging issues early gives them time to correct before the W-2 goes out.
Bring specific numbers. "My YTD 401(k) shows $18,400 but I've been contributing 10% of $90,000, which should be $9,000" is an actionable complaint. "My W-2 looks wrong" is not.
If the correction happens after the W-2 is issued, your employer will need to file a W-2c (corrected W-2). This is normal and not a big deal, but it does delay your tax return — you need the corrected version before filing.
Tips for making this easier next year
The year-end review is a lot easier if you've been tracking your stubs throughout the year. Whether you're using a spreadsheet, a tool like StubSheet (disclosure: I built it), or just keeping PDFs in a folder, having your stub data available makes the December check a 20-minute exercise instead of a two-hour PDF excavation.
If you never tracked stubs during the year, the December review is still worth doing — you just have more work to do to gather the data. Pull your YTD numbers from your most recent stub and compare them against your expectations and against any records you do have (bank deposits, 401(k) plan statements, benefit elections).
Most of all, do the review. Twenty minutes in December saves real pain in February.
The short version
Check YTD gross, all major tax withholdings, 401(k) and HSA contributions, benefits deductions, and net pay against your expectations for the year. Watch for missing retro pay, phantom deductions, and changes that never propagated. Flag anything unusual with payroll before the W-2 is issued. Twenty minutes of effort that can save weeks of hassle at tax time.