The problem
A founder who joins a project at roughly 70% built is asked a question they cannot answer: what share do you want? Advice online is a list of percentages and rules of thumb, and none of it shows what "80/20, four-year vest, one-year cliff" does to each person across the scenarios that matter. Most never see the case that decides it: someone leaves in month eleven, or month thirty.
So the number gets negotiated on feelings. The person with less leverage tends to accept whatever feels polite, and the consequences surface a year later, when it is expensive and personal to renegotiate.
Why now
Small teams now get to a working product in weeks, so a founder can join a project that is already substantially built. That makes the late-joiner question common and sharp: how do you credit work already done without handing the newcomer a cliff-free windfall? Meanwhile equity discussion has moved out of lawyers' offices and into public threads, where people ask for exactly this kind of picture and receive percentages in reply. The arithmetic is simple enough to run in a browser, and what has been missing is a view of it that a non-lawyer can drag.
What it is
One page, one chart. Two founders' vested equity stacks month by month, with the unvested remainder shown as the pool. Sliders set the split, the vesting length, the cliff and a head-start credit for the founder who began earlier. A marker you drag sets the month someone leaves, and a table states what that person walks away with and what returns to the pool.
Three scenarios are preloaded, including a late joiner and a departure just before the cliff. The demo does only straight-line vesting for two people. It does not model dilution, tax, or cash contributed, and it produces no document.
Who it's for
The founder on the weaker side of the table, usually the non-technical one who joined later and has no template to push back with. It is also for the founder who started first and wants to offer something that will still feel fair in a year.
It is not for lawyers or for companies with investors, option pools and multiple rounds. They need cap-table software, and a two-person simplification would mislead them. It is also not an advice engine: it shows consequences and never recommends a split.
How it makes money
It does not yet, and that is correct for a tool a founder needs once, at the moment of a hard conversation. A subscription fails for that reason, and ads would taint the one thing the page offers, which is neutrality.
The realistic routes are adjacent: a paid export that turns the chosen terms into a plain-language summary a lawyer can start from, or a referral arrangement with startup-focused legal-form providers. Either is only worth building after seeing how many visitors want to take the next step.
Go to market
Post it where the question is already being asked. Founder-matching threads and the equity-split discussions in startup subreddits get the same question every week, and a link that answers it with a picture gets forwarded by the people replying. The first audience is the late joiner, who will send the link to their co-founder with the scenario already loaded.
Second, founder-matching programmes and accelerator office hours, which repeat the same advice in every cohort and would rather point to a page than re-explain a cliff.