Generally - if you're in debates with potential investors and you want to find out what (if any) interest rate should be applied to the funding, it will always be a part of the negotiation. There is no specific number you can agree on with your investors, but mutual agreement has to be made to have a successful cooperation with your investor. Your guide could be saas business valuation calculator, which will help determine the potential value of your business based on Annual Recurring Revenue and Growth per year. This tool might offer some assistance.