Enter your plan's terms — see the per-paycheck cost, the value at purchase, and the effective return the plan hands you.
If you sell at purchase
—
| You buy at | — |
| Per-paycheck set-aside (biweekly) | — |
| Contributed per 6-month period | — |
| Effective return on contributions | — |
Discount gains are taxed as ordinary income when you sell immediately. Not investment advice — the math is the plan's, the decision is yours.
The ESPP math
buy price = (lookback ? min(start, end) : end) × (1 − discount)
gain = shares × (market − buy price)
The discount is the guaranteed part; the lookback is the upside kicker. In a rising period the lookback buys at the old, lower price; in a falling period you still get the discount off the new, lower price — heads you win more, tails you still win.
A worked example
10% of a $90,000 salary is $4,500 per 6-month period ($346 per biweekly check). Stock went $50 → $58 with a 15% lookback plan: you buy at $42.50, receive ~105 shares worth $6,141, and an immediate sale banks ~$1,641 — a 36% return on money that was parked for at most six months. Even flat stock returns 17.6%.
Where ESPP fits in the order of operations
The standard priority stack: 401(k) to the full match first (free 100%), then ESPP to the max if you can float the paycheck reduction (the contributions come back with profit at each purchase), then everything else. Pair with the 401(k) per-paycheck calculator to see both set-asides against your take-home at once.
Frequently asked questions
Is an ESPP worth it?
With a 15% discount and immediate selling, almost always — a 15% discount is a ~17.6% gain on the day shares hit your account, repeated every purchase period. It's routinely called the best guaranteed return in personal finance after a 401(k) match.
What is an ESPP lookback?
The best plans apply your discount to the LOWER of the price at the period's start or end. If the stock rose from $50 to $65 during the period, you buy at 15% off $50 ($42.50) while shares trade at $65 — a 53% gain. Lookback turns a good perk into a great one.
Should I sell ESPP shares immediately?
Selling immediately locks the discount as a nearly risk-free gain (taxed as ordinary income on the discount portion). Holding for qualifying disposition (2 years from grant, 1 from purchase) can shift some gain to capital-gains rates but adds single-stock risk on top of the paycheck you already get from the same company. Many planners prefer sell-and-diversify.
How much can I put in an ESPP?
Plans typically allow 1–15% of salary, with an IRS cap of $25,000 of stock value per calendar year. The calculator shows the paycheck impact of whatever percentage you pick.