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Valuation of a startup is estimating the worth of it . Pre-money valuation is used by venture capitalist and private equity  before the company receives any financing. There can be a few rounds of financing for a corporation. Investors such as venture capitalist, private equity, or angel investors may use this valuation in order to evaluate how and how much to invest.
Post-money valuation is the value of a corporation after some money has been invested in a corporation . This valuation takes into account the pre-money valuation and any new investment.