October 23, 2026
Start by checking your authorized shares, because most startups have already used nearly all of them. If the new co-founder's shares don't fit, the board and stockholders first approve an amendment to the certificate of incorporation increasing the authorized shares, the company files it in Delaware, and only then does the board issue the new shares. The new co-founder signs a restricted stock purchase agreement and a CIIAA, with vesting that starts on the day they join and an 83(b) election filed within 30 days of the issuance if they buy stock. Issue new shares rather than taking them from the employee option pool, and price them at par only if the company still has no value; otherwise use the 409A price or grant options.
Key takeaways
There's no formula. Start from what the person is bringing and what is left to build: a technical co-founder joining before the product exists is in a different position from a commercial co-founder joining after launch. Then model it. Every new share dilutes the existing founders, any existing stockholders and the pool's share of the company in the same proportion, so look at both the issued-share percentages and the fully diluted percentages before anyone sees an offer. Offer an exact number of shares, not a percentage, because percentages change with every issuance. See Founder Equity: How To Split Equity Among Co-founders and How Do I Pick a Co-founder?
This is the most common problem we see when founders add a co-founder, and it has to be solved before anything is signed. The certificate of incorporation sets a hard limit on the number of shares the company can issue. A typical formation authorizes 10,000,000 shares, issues 8,000,000 to the founders and reserves 1,000,000 for the option pool. That leaves 1,000,000 shares, and the ungranted part of the pool doesn't count as available, because it is already reserved under the equity incentive plan. Companies formed on an online platform or by the founders themselves often have even less room, because they authorized exactly what they issued. So a third co-founder with a meaningful stake almost never fits.
The company can't simply issue the shares anyway. Under Delaware law, shares issued beyond the number the charter authorizes are void, and fixing an overissue later takes a formal ratification process that is slower and more expensive than doing it in the right order. Investors and their counsel check this in diligence. The fix is to amend the certificate of incorporation to increase the authorized shares first, and issue the new co-founder's stock only after the amendment is effective.
The process has five steps, and the order matters. Our page on How Do I Increase My Startup's Authorized Shares? covers each one in more detail.
First, calculate the number you need. Add up every share that is issued or spoken for: the issued and outstanding shares, the full option pool (granted and ungranted), any shares reserved for warrants, and, if you have preferred stock, the common reserved for its conversion. Add the new co-founder's grant. That total is the minimum the charter must authorize. SAFEs and convertible notes don't need authorized shares until they convert, and they convert in a priced round, where the new charter handles it. Then add some headroom for the next few grants so you aren't amending again in three months. Keep the increase reasonable, because under Delaware's default authorized shares method the franchise tax bill rises with every authorized share. Most startups file under the assumed par value capital method instead, which keeps the tax low. See Delaware Franchise Tax.
Second, the board approves the amendment. The board adopts a resolution setting out the new authorized share count and declaring the amendment advisable, usually by unanimous written consent. See Startup Board Consent.
Third, the stockholders approve it. For a private company, an increase in authorized shares generally needs the approval of a majority of the outstanding voting stock, and usually this is done by written consent. When the only stockholders are the founders, that is simply the founders' signatures. Who else has to sign depends on your cap table: a class of stock may get its own vote unless the charter opts out, preferred stock often has protective provisions giving it a veto over an increase, and a voting agreement may commit investors to vote a certain way. The one common exception is a forward stock split with a proportionate increase, which the board can approve alone while the company has only one class of stock. See What Do Stockholders in My Startup Need to Approve?
Fourth, file the certificate of amendment in Delaware. An officer signs it and the company files it with the Division of Corporations, usually through its registered agent. It takes effect when it is filed unless it states a later time.
Fifth, issue the new co-founder's shares. Once the amendment is effective, the board approves the issuance: the number of shares, the price, the vesting schedule and its fair market value determination. Many companies use a second board consent dated after the filing so the record shows the order clearly. The issuance date is the date the shares are actually issued, and that is when the new co-founder's 30-day window for the 83(b) election starts.
Example. A company has 10,000,000 authorized shares. Two founders hold 4,000,000 each, and the option pool reserves 1,000,000, of which 250,000 have been granted. The founders want to add a third co-founder with 1,500,000 shares of restricted stock. The company needs 8,000,000 + 1,000,000 + 1,500,000 = 10,500,000 authorized shares, which is 500,000 more than it has. It decides to increase to 12,000,000, leaving 1,500,000 unreserved shares for future grants or a pool increase. The board approves the amendment by written consent, both founders sign a stockholder consent (as holders of 100% of the stock, no notice to other stockholders is needed), and the company files the certificate of amendment. The next day, the board approves the issuance of 1,500,000 shares to the new co-founder, who signs the RSPA and CIIAA and files an 83(b) within 30 days.
| Holder | Shares | Before (issued) | After (issued) | After (fully diluted) |
|---|---|---|---|---|
| Founder A | 4,000,000 | 50.0% | 42.1% | 38.1% |
| Founder B | 4,000,000 | 50.0% | 42.1% | 38.1% |
| New co-founder | 1,500,000 | 15.8% | 14.3% | |
| Option pool | 1,000,000 | 9.5% | ||
| Total | 10,500,000 | 100.0% | 100.0% | 100.0% |
Issued shares rise to 9,500,000, so each original founder falls from 50% to 4,000,000 ÷ 9,500,000 = 42.1%. Fully diluted, counting the full pool, the total is 10,500,000: each original founder holds 38.1%, the new co-founder 14.3% and the pool 9.5%. Before the issuance, fully diluted, each original founder held 44.4% of 9,000,000 shares. The 1,500,000 unreserved authorized shares don't count in either percentage until they are issued or reserved.
Usually not. The option pool is reserved under the equity incentive plan for employees, advisors and consultants. Granting a co-founder a large block from it leaves too little for the hires the pool was sized for, and investors will ask you to top it up in the next round, usually at the founders' expense. Using the pool also doesn't solve the authorized share problem for long, because a depleted pool has to be refilled, which takes the same charter amendment. A co-founder gets a new issuance of restricted stock from authorized shares that aren't reserved for the pool.
The exception is someone who is really an early employee with a co-founder title, joining after the company has raised money and taking a smaller stake. For that person, a grant of options or restricted stock under the plan may be the right instrument. The label matters less than the role, the size of the stake and when they join.
If the company still has no real value, meaning no revenue, no funding and no product, the board can document that and sell the shares at par, $0.00001 per share. In the example, the new co-founder pays 1,500,000 × $0.00001 = $15.00, signs a restricted stock purchase agreement (RSPA), pays by check or wire and files an 83(b) election within 30 days of the issuance date.
Once the company has value, the board should get a 409A valuation and sell the stock at that price. After a SAFE round the gap between par and the 409A price can be large, and a co-founder buying 1,500,000 shares at even $0.10 a share would have to pay $150,000. That's why late co-founders often receive stock options with an exercise price equal to the 409A value, paying nothing at grant. Options need authorized shares too, reserved under the plan, so the amendment question doesn't go away. Issuing stock below its fair market value in exchange for services creates compensation income under Section 83 of the Internal Revenue Code, so don't paper over the gap with a low price. Talk to a tax advisor about which route fits. See 409A Valuation.
Use the same structure as the original founders: four-year vesting from the date the new co-founder joins, with a one-year cliff. If they did meaningful work before joining, such as months of part-time product work, you can set the vesting commencement date earlier, but only if everyone agrees and it's written into the RSPA. Informal work done before the person was a founder doesn't earn credit on its own. If the new co-founder is getting options, the same vesting schedule goes into the option grant. See Vesting Schedule.
If you need more authorized shares, the set starts with the board consent approving the charter amendment, the stockholder consent approving it and the filed certificate of amendment. Then comes the board consent approving the issuance or grant, the number of shares, the price, the vesting schedule and the board's fair market value determination. The new co-founder signs an RSPA, or an option agreement under the plan, with the vesting schedule and the company's repurchase right on unvested shares, and a CIIAA assigning any IP they created for the company, including work done before they formally joined. If they're buying stock, they pay the purchase price by check or wire and file an 83(b) election within 30 days of the issuance date, giving the company a copy. Then update the stock ledger and cap table.
If the founders have a founders' agreement, update it, and settle titles, roles and decision-making in writing, including whether the new co-founder joins the board. See RSPA and 83(b) Election.
A standard post-money SAFE doesn't restrict new issuances or give SAFE holders a vote on a charter amendment, but check any side letters, convertible notes and the terms of any priced round. Once there is preferred stock, the certificate of incorporation's protective provisions often require the preferred to approve an increase in authorized shares, new classes of stock or increases in the pool, and some require approval for any issuance outside the plan. Under a post-money SAFE, the new co-founder's shares dilute the existing founders, not the SAFE holders. Raise the change with your investors early.
Have this conversation before the paperwork is signed. With standard vesting, the company can repurchase unvested shares at the price paid if the co-founder leaves, and vested shares stay with them. Talk about what each person expects, whether there should be any acceleration, and how the company would handle a departure in the first year. See What Happens to a Co-Founder's Equity When They Leave?
For more, see How Do I Increase My Startup's Authorized Shares?, Certificate of Incorporation, Equity Dilution and What Is a Cap Table?
To check your authorized shares before you make a co-founder an offer, contact us.
