Start with the use of funds
An idea alone does not establish a market price. Describe the customer problem, what has been tested, the next milestone, the budget needed to reach it and the assumptions that could fail. A funding request is the amount required for a plan; a valuation is a negotiated transaction term. They should not be presented as the same figure.
Make the ownership calculation explicit
In a simplified priced-equity example, a company valued at 900,000 before a new investment of 100,000 has a post-money value of 1,000,000; the new investor holds 10% if there are no other changes. This is arithmetic, not an estimate of any company's value. Existing convertibles, option pools, fees and negotiated rights can change the actual result.
Distinguish the instrument from the headline
A priced share issue, a convertible note and a SAFE do not create identical rights. YC's documents explain that its SAFE is a future-equity contract rather than a loan. Before agreeing terms, model ownership under plausible later rounds and check which legal form applies to the parties and jurisdiction. No fixed financing sequence or universal valuation multiple is assumed here.