NUA Cost Basis: How to Find It, Verify It, and Use It in Your Planning

Cost basis is the single number that determines whether your NUA election is transformative or marginal. A $1M stock position with $50K basis saves you dramatically more than the same position with $600K basis. Yet most employees approaching retirement either don't know their cost basis or assume it's the same as what they'd find in a brokerage account. In a 401(k), it isn't.

What cost basis means in NUA (it's different)

In a normal brokerage account, "cost basis" means what you paid for shares — your out-of-pocket investment. In a 401(k) NUA context, cost basis means something different: what the plan paid to acquire the shares on your behalf, as recorded in the plan's books.

This distinction matters for three reasons:

• You didn't "buy" the stock yourself. For employer match shares and profit-sharing contributions, the employer purchased the stock for your account. Your cost basis is the price they paid on the date they bought it — not the current market value, not the price at vesting.
• The plan's records control. The IRS looks to the plan's own records to determine basis for NUA purposes. Whatever the plan's books show is your cost basis under IRC § 402(e)(4).¹ You cannot substitute a higher number even if you believe the plan's tracking is wrong — you'd need to get the plan administrator to correct it.
• It's taxed as ordinary income in the year of distribution. The cost basis is the "price" you pay upfront to access the favorable capital gains treatment on the NUA appreciation. Low cost basis = small ordinary income bill in year 1, large capital gain deferred to whenever you sell.

How employer stock cost basis is established

Most 401(k) plans accumulate employer stock through multiple contribution types, each tracked separately:

Employer match contributions

When an employer matches your 401(k) contributions with company stock, the plan purchases shares on the open market (or allocates treasury shares) at the prevailing price. The cost basis for these shares is the price on the date of purchase, as recorded in the plan's books. If your employer bought 10 shares at $40/share five years ago as a match, those 10 shares have a cost basis of $400 — even if they're worth $8,000 today.

Employer profit-sharing and ESOP contributions

In profit-sharing plans and ESOPs, the plan itself often holds a large block of employer stock. Shares are allocated to participant accounts periodically. The cost basis is typically the price at which the shares were allocated to your account, per the plan's records. ESOP shares contributed by the employer at zero cash cost to the plan are often tracked at a nominal basis — sometimes $0 or a very low administrative value — making ESOP NUA elections particularly powerful.

Employee after-tax purchases

Some 401(k) plans allow participants to direct after-tax contributions into employer stock. If you voluntarily bought employer shares inside your plan, those shares have a different cost basis from match or profit-sharing shares. The plan should track these separately. For NUA purposes, after-tax contributions increase your cost basis, which slightly reduces the NUA advantage — but they're still eligible for NUA treatment.

Lot tracking

Plans track employer stock by lot — separate blocks of shares, each with a purchase date and cost basis, accumulated over years of contributions. A 30-year employee might have dozens of lots at different prices. The plan aggregates these for NUA reporting: your total cost basis is the sum of all lot bases, and the NUA is market value at distribution minus that total basis.

For partial NUA strategies (NUA-ing only high-appreciation lots and rolling lower-appreciation lots), you need lot-level data. See Partial NUA Strategy for how to use lot-level information to optimize the split.

Why cost basis determines NUA's value

Cost basis affects NUA's tax advantage in a simple way: the lower the basis as a percentage of market value, the more of the position converts from ordinary income to long-term capital gains, and the greater the tax savings.

^† Approximate federal savings assuming 37% ordinary rate on rollover vs 20% LTCG + 3.8% NIIT on NUA. State taxes, IRMAA, and timing effects not included. Model your exact numbers using the NUA vs Rollover Calculator.

There's no hard rule for when NUA "isn't worth it" on the basis percentage alone — because marginal tax rate, state taxes, estate planning goals, and holding timeline all interact. But as a rough guide: cost basis below 25% of market value almost always makes NUA compelling; above 60–70%, the advantage narrows and the analysis becomes more sensitive to other factors.

How to request your cost basis from the plan

Your plan administrator — typically the 401(k) recordkeeper (Fidelity, Vanguard, Schwab, Empower, Merrill, etc.) — is required to track and provide your cost basis in employer stock. Here's how to get it:

Step 1: Log into your account

Most major recordkeepers display employer stock holdings in your account dashboard. Look for a line item labeled "Employer Stock," "Company Stock," or the ticker symbol of your employer. Many platforms show the cost basis alongside the market value in the position detail. However, not all recordkeeper platforms surface lot-level data in the web interface — you may need to call or submit a written request.

Step 2: Request an NUA cost basis statement

Call or email your plan's customer service line and ask specifically for:

"I am considering a qualifying NUA distribution under IRC § 402(e)(4). I need my plan's cost basis in employer securities — specifically the per-share or aggregate basis as tracked by the plan for NUA reporting purposes, including lot-level detail if available."

Use the IRC citation. Recordkeeper representatives don't always know what NUA is, but they do know how to route IRC-referenced requests to the right team. Ask for the response in writing (email or mailed statement).

Step 3: Verify the basis figure

When you receive the cost basis figure, check it against what you'd expect. If you've held employer stock for 25 years and the basis is very low (often under 10% of market value for long-tenure employees at companies with strong stock appreciation), that's consistent. If the basis seems surprisingly high, request the lot-level breakdown — a plan may be including shares that were contributed at a time when the stock price was elevated, or there may be a tracking error worth investigating before you execute.

Step 4: Get it in writing before you execute

Your NUA cost basis will appear in Box 2a (taxable amount) and Box 6 (NUA) of the 1099-R issued by the plan after distribution. Reconcile the 1099-R values against what the plan told you before distribution. Discrepancies between what the plan quoted and what appears on the 1099-R can complicate your tax return and may require a corrected 1099-R — easier to resolve before the distribution than after.

The 20% withholding problem

Under IRC § 3405(c), plans are required to withhold 20% on eligible rollover distributions — and the cost basis portion of an NUA distribution is an eligible rollover distribution.² This creates a practical complication: you can't withhold 20% from stock shares.

Plans handle this in one of two ways:

• Withholding from the non-stock portion. If your lump-sum distribution includes cash, money market funds, or other non-stock assets, the plan typically withholds 20% of the cost basis from that liquid portion. Example: cost basis is $150,000, so the plan withholds $30,000 from the cash being distributed alongside the in-kind stock transfer.
• Requiring you to provide funds. Some plans require you to send in a check or authorize an ACH to cover the mandatory withholding if there isn't enough non-stock liquid in the lump-sum to cover it.

The withheld amount is credited against your tax liability — it's not a separate tax, just prepayment. If your actual tax bill on the cost basis is more or less than 20%, you'll true up on your return. But be aware: if the plan withholds $30,000 and your actual tax on the cost basis is $45,000, you'll owe a further $15,000 at filing plus potential estimated tax underpayment penalties.

Worked example: two employees, same stock

David and Carol both work at the same company. Both have exactly 1,000 shares of employer stock in their 401(k), now worth $800 per share ($800,000 total). The difference: David joined 30 years ago; Carol joined 10 years ago. David's shares were purchased by the plan at an average of $28/share. Carol's shares were purchased at an average of $310/share.

Simplified example. Both pay 37% in IRA scenario. NUA path uses 24% ordinary income on basis + 23.8% max LTCG+NIIT on NUA layer. Actual rates depend on income in each year; model your own situation in the NUA vs Rollover Calculator.

The intuition: even though Carol has much higher cost basis ($310K vs $28K), her NUA advantage is similar to David's — because the rate differential (37% ordinary vs 23.8% LTCG+NIIT) applies to a large amount in both cases. What changes is when and how much she pays: Carol's upfront ordinary income bill is much larger ($310K taxable in year 1 vs $28K). That creates a higher cash-flow burden at distribution, which matters for planning even if the lifetime math is similar.

This is why cost basis isn't just a "big number good, small number bad" calculation — it shapes the year-1 cash impact and the withholding mechanics, not just the total lifetime tax comparison.

When cost basis is unknown or disputed

Plan recordkeepers can lose basis data. This happens in three common scenarios:

• Plan conversions. When a plan moves from one recordkeeper to another, historical lot data doesn't always transfer cleanly. Shares acquired before the conversion date may appear in the new system with a missing or incorrect basis.
• Old employer stock from a merger or acquisition. If your employer was acquired and the legacy company's shares became shares of the acquirer, the original lot basis may not have survived the transition. The plan's current records may show only the shares at the merger-exchange price, which could be higher or lower than the original purchase price.
• Pre-digital records. For employees who've held shares since the 1980s or early 1990s, paper records may have been lost when the plan moved to electronic recordkeeping.

What to do if basis is missing: There is no IRS safe harbor for estimated NUA cost basis — you cannot simply assume $0. If the plan cannot provide documentation of cost basis, you have a few options:

1. Request the plan to research it. Plans have an obligation to maintain records. Ask in writing and give them time to investigate before concluding the data is gone.
2. Work with a tax advisor to reconstruct basis from available evidence. Historical stock prices, employment records, contribution statements, and prior Form 5500 filings can sometimes be used to reconstruct reasonable basis figures. This requires documentation and judgment — it's not a do-it-yourself exercise.
3. Request a corrected 1099-R if you believe the plan's basis is wrong. The plan must issue a corrected 1099-R if the original is inaccurate. If the plan refuses, you can contest it with the IRS, though that's a time-consuming process.

If basis genuinely cannot be determined, some advisors conservatively default to treating the full distribution as ordinary income (as if rolling to an IRA), forgoing the NUA election. This is the cautious approach; the right answer depends on how much documentation can be recovered and the magnitude of the potential tax savings.

Talk to an NUA specialist before you execute

Cost basis is the number everything else is built on. Getting it right — requesting it from the right source, verifying the lot-level data, modeling the withholding impact, and confirming it on the 1099-R — is the foundational step before any NUA decision. A fee-only NUA specialist will walk through this with you in advance, not after the distribution is done.