Updated July 28, 2026. Quick answer: Capture the full 401(k) match first — that is an immediate guaranteed return no ESPP discount beats. After the match, an ESPP with a lookback sold immediately is usually the next best dollar, ahead of unmatched 401(k) contributions.
The ordering most situations produce
- 401(k) to the full match. An immediate guaranteed return on the matched portion. Nothing else in the list competes.
- ESPP with a lookback, sold at purchase. A discount off the lower of two prices, realised in months rather than decades, with almost no market risk if you sell immediately.
- Unmatched 401(k). Tax deferral, but the money is locked up for decades.
What flips the order
- No lookback and a small discount. The ESPP advantage shrinks toward the discount alone and the comparison gets close.
- You would hold the shares. Then it is not a discount trade, it is a concentrated stock purchase, and the guaranteed-return logic no longer applies.
- Cash flow. ESPP contributions are after-tax and tie up money until purchase; 401(k) contributions reduce this paycheck’s tax immediately.
The comparison assumes you actually sell at purchase. Every calculation showing the ESPP winning depends on that, and it is exactly the step people skip.
Sources
IRC §423(b)(6), (b)(8); IRC §402(g) (elective deferral limit); IRC §401(m) (matching contributions).
This states what the cited authority says. It is not tax advice.