Stock Option Vesting Schedule Calculator

Stock option vesting schedules (and why the details matter)

Employee stock options (and RSUs) often come with a vesting schedule—a timeline that determines when you earn the right to exercise options or receive shares. Vesting is designed to reward continued employment: you generally do not own the equity immediately on grant day, you earn it over time. Knowing your vesting schedule is useful for planning (exercise costs, taxes, diversification), negotiating offers, and understanding what you would keep if you left the company on a specific date.

This calculator generates a simple monthly vesting schedule from four inputs: total options, vesting start date, cliff length (months), and total vesting length (months). It then shows how many options vest each month and the cumulative total vested over time.

Key terms (quick definitions)

• Total options: the size of your grant (the maximum options you can earn if you stay through the full schedule).
• Vesting start date: the date the vesting clock begins (often your start date, sometimes a grant date; confirm your agreement).
• Cliff: an initial period where nothing vests. At the end of the cliff, a larger “catch-up” amount typically vests at once.
• Vesting months: the total duration over which the grant becomes vested (commonly 48 months for a 4-year schedule).
• Monthly vesting: vesting happens in equal installments each month after the cliff (or with a cliff catch-up then equal monthly amounts).

How the monthly vesting math works

There are different ways companies implement vesting details, but the most common pattern for options is:

1. No vesting occurs before the cliff ends.
2. At the cliff date, the amount that would have vested monthly up to that point vests all at once (the “catch-up”).
3. After the cliff, the remaining options vest in equal monthly installments until the end of the vesting period.

Let:

• N = total options granted
• M = total vesting months (the full schedule length)
• C = cliff months
• m = month number since vesting start (1, 2, 3, …)

A simple cumulative vesting model is:

• If m < C: cumulative vested = 0
• If m ≥ C: cumulative vested = N × (m / M), capped at N

The amount vesting in month m is then:

• monthly vested(m) = cumulative(m) − cumulative(m−1)

In MathML form, the cumulative vested function can be expressed as:

with the additional rule that V(m) = 0 for m < C.

Rounding: why schedules sometimes show uneven months

Options are whole numbers, but N/M is often not an integer. Real schedules therefore need a rounding rule. A common approach is:

• Compute cumulative vested each month (possibly as a fractional number).
• Round down cumulative vested to a whole option each month.
• Ensure the final month reaches exactly N by assigning any remainder to the last vesting month.

This prevents “over-vesting” early and guarantees the schedule ends at exactly the grant size.

How to interpret the results

Your schedule will typically show columns like:

• Vesting date: the date each monthly vest happens (often the same day-of-month as the start date; policies vary).
• Options vested this month: what you earned in that period (0 before the cliff, a larger number at the cliff if catch-up applies).
• Cumulative vested: total options earned so far.
• Unvested remaining: N − cumulative vested.

If you’re planning a job change, the most important figure is typically the cumulative vested as of your expected end date (and what remains unvested that you would forfeit under standard terms).

Worked example (4 years with a 1-year cliff)

Suppose you receive 4,800 options, with:

• Vesting start date: 2026-01-15
• Cliff: 12 months
• Total vesting: 48 months

Monthly rate (ignoring rounding) is 4,800 / 48 = 100 options per month. Nothing vests in months 1–11. At month 12 (the cliff), you typically vest 12 × 100 = 1,200 options at once. After that, you vest ~100 options per month until month 48.

So:

• After 11 months: 0 vested
• At the 12-month cliff: 1,200 vested total
• At 24 months: 2,400 vested total
• At 48 months: 4,800 vested total

Common schedules compared

Assumptions and limitations (important)

This calculator is a planning tool and uses a simplified vesting model. Your actual plan documents control. In particular:

• Monthly vesting only: The schedule assumes vesting occurs in monthly increments. Some plans vest quarterly, annually, or on specific company-defined dates.
• Cliff behavior: It assumes no vesting before the cliff and a catch-up vest at the cliff consistent with monthly accrual. Some plans define the cliff vest date differently (e.g., exactly one year after start, or the next monthly vest date after one year).
• Date conventions vary: Companies may define vest dates as the last day of the month, a fixed day (e.g., the 1st), or the anniversary day. If your start date is on the 29th–31st, some months may shift.
• Rounding rules differ: This page may round monthly/cumulative vesting to whole options and true-up at the end. Your plan may round differently (e.g., round each installment, or round at the end of each year).
• No acceleration: This does not model single-trigger or double-trigger acceleration on acquisition/termination events.
• No employment termination rules: Real outcomes depend on your last day of employment, any notice period, and whether vesting happens if you leave between vest dates.
• No exercise/expiration/tax modeling: This does not compute exercise costs, AMT, withholding, ISO vs NSO differences, post-termination exercise windows, or expiration dates.
• No refresh grants or multiple grants: This is for one grant at a time (though you can run it multiple times and combine results externally).

Not legal or tax advice. Equity compensation is complex; confirm details with your plan documents and qualified professionals.

Using the calculator (step-by-step)

1. Enter your Total Options (the grant size).
2. Choose your Grant Start Date (the vesting start date).
3. Enter Cliff Months (often 12; use 0 if there is no cliff).
4. Enter Vesting Months (often 48 for four years).
5. Select Create Schedule to generate monthly vesting rows and totals.