Founder Cliff Acceleration Calculator
Model your vested shares, cliff status, and accelerated equity in single-trigger and double-trigger acquisition scenarios.
What Is Founder Vesting and the Cliff?
Founder vesting is the schedule by which a founder earns their equity over time, rather than owning it all upfront. The industry standard is a 4-year vesting schedule with a 1-year cliff: no equity vests for the first 12 months, then 25% vests on the cliff date, and the remaining 75% vests monthly (1/48 per month) over the next 36 months. The cliff exists to ensure founders are committed before any equity changes hands. According to the National Venture Capital Association's model documents, the 4-year/1-year cliff structure is used in over 90% of VC-backed US startups. Last updated: May 2026.
Single-Trigger vs Double-Trigger Acceleration
Acceleration provisions determine what happens to unvested founder shares at an acquisition. Single-trigger acceleration vests all remaining shares immediately when the acquisition closes — founders get 100% of their equity regardless of whether they stay post-acquisition. Acquirers often resist this because it removes retention incentive. Double-trigger acceleration is more founder-friendly in a balanced way: unvested shares only accelerate if both an acquisition occurs AND the founder is terminated without cause or forced to resign for good reason within a defined window (usually 12 months). Double-trigger is now the market standard recommended by most startup attorneys and VC model documents as a fair compromise between founder protection and acquirer retention needs.
How to Use This Calculator
Enter total founder shares issued at company formation (not options — actual founder stock). Enter the cliff period (12 months is standard; 0 if your agreement has no cliff). Enter months served since your vesting start date — typically the company formation date or your start date as specified in your Founder Stock Purchase Agreement. Select your acceleration type from the dropdown. The calculator shows vested shares under normal time-based vesting, unvested shares remaining, whether you have cleared your cliff, and how many additional shares would accelerate in an acquisition scenario. This output is informational — always have a startup attorney review your specific agreements before any transaction.
Frequently Asked Questions
What is a founder cliff in a vesting schedule?
A cliff is a minimum service period before any equity vests. The standard founder cliff is 12 months — if a founder leaves before month 12, they receive zero equity. At month 12, the full first-year tranche vests at once (25% of 4-year total). After the cliff, vesting is monthly.
What is single-trigger acceleration?
Single-trigger acceleration means unvested shares accelerate — vest immediately — upon a single event, usually a change of control (acquisition or merger). The acquiring company often objects because it removes retention incentive for key founders post-acquisition.
What is double-trigger acceleration?
Double-trigger acceleration requires two events: (1) a change of control AND (2) termination without cause or resignation for good reason within 12 months post-acquisition. It is the standard preferred by VCs and acquirers as it balances founder protection with retention.
How is founder vesting calculated on a standard 4-year schedule?
Standard calculation: vested shares = (months served / 48) × total shares. Before the 12-month cliff, 0 shares vest. At month 12, 25% vests. After the cliff, 1/48 of total shares vests each month until month 48. Source: NVCA model documents.
Can an acquirer cancel unvested founder shares?
Yes. Without acceleration provisions, an acquirer can allow unvested shares to lapse or convert them to earn-out arrangements tied to continued employment. This is why negotiating at least double-trigger acceleration at founding is critical. Always have a startup attorney review agreements before an acquisition.