Employee Stock Purchase Plan (ESPP) Calculator

An employee share purchase plan lets staff buy their employer's shares at a set discount to the market price, funded by deductions taken from pay across an offering period. The discount is the whole of the immediate benefit: nothing here depends on the share price going up.

How the discount turns into a return

The arithmetic catches people out, because a discount off the market price is worth more than the same figure as a return on what was paid. At a 15% discount, 6,000 of contributions buys shares at 85 rather than 100, which is 70.5882 shares worth 7,058.82 at the market price. The gain is 1,058.82, and against the 6,000 actually contributed that is 17.65%, not 15%. The general form is d divided by one minus d: a 10% discount returns 11.11%, a 15% discount returns 17.65%, a 20% discount returns 25%.

A worked example

Contribution per period 500, twelve periods, a share price of 100 and a 15% discount. Total contributed 6,000. Purchase price 85. Shares acquired 70.5882. Market value at purchase 7,058.82. Immediate benefit 1,058.82, a 17.65% return on what went in.

Selling at purchase against holding

Selling at the purchase price on the purchase date converts the discount to cash and ends the exposure to the share price. That is the cleanest version of the arithmetic above, and it is not always available: many plans impose a delay between purchase and the first permitted sale, and during that window the share price moves like any other. Holding on adds ordinary share price exposure on top of the discount, in the shares of the same company that already pays the salary.

That last point has been studied. Work on company stock inside employer retirement plans reports that participants systematically underestimate the risk of employer stock and lean on its past performance when deciding how much to hold. The finding is about retirement plan balances rather than purchase plans, but the position it describes is the same one: pay, and savings, riding on a single employer.

What the discount actually is

The discount is a form of pay, not a market return, and accounting treats it that way. A plan like this falls under the international standard for share-based payment, which requires the effects of share-based payment transactions with employees to be reflected in the employer's reported profit or loss.

Tax is outside the model and varies widely. In most systems the discount is treated as employment income at some point, and how much of any later gain counts as an investment gain often depends on how long the shares are held after purchase. Plans differ, jurisdictions differ, and the figure this calculator shows is before any of it.

What the calculator leaves out

• A lookback feature, where the purchase price is set from the lower of the offering-date and purchase-date prices, which raises the effective discount by an amount that depends entirely on how the price moved
• Caps on participation, whether as a share of salary or an absolute amount, which are set by the plan and by local rules
• Any waiting period between purchase and the first permitted sale, and any movement in the share price across it
• Tax and payroll withholding on the discount
• Dealing costs and currency conversion on sale
• Whether the contributions would have been doing something else in the meantime

For educational illustration only

This calculator divides total contributions by a discounted purchase price, values the resulting shares at the undiscounted price, and reports the difference. It assumes the discount and the share price both hold steady across the offering period, and that shares are bought in one go at the end. The output is the arithmetic of the discount at one price, not a projection of what a holding will be worth.