What's a generally acceptable founder's premium for the original founder of a tech startup in terms of equity percentage.
Original Founder: Ideas and key concepts behind the start-up, design the architecture, sacrifices early on, few months of dedication towards the startup before any of the co-founder were brought in.
Also in other words, how much is an idea worth.
Ideas aren't worth squat in my opinion. The landscape is littered with the corpses of companies that couldn't execute their ideas.
But it sounds like what you're asking for is how much equity you should get for the work you've already done. That's easier, just tally up the hours, apply a rate and, presto chango, there it is.
That's basically what each late investor should put on the table for equal equity. Anything they bring beyond that value should give them more equity than you.
That's in a perfect economics-is-mathematics world. You should be able to argue for more of the pie than that but, since you almost certainly approached them, they have an argument that you need them more than they need you.
Unless you opt for equal equity where the value of your initial efforts plus your cash injection matches their cash injection, you'll always have an issue valuing the difference. In fact, they'll probably argue over the rate you use in paragraph two above. You'll have to negotiate those inexact values without our help since we have no idea what your 'product' is let alone its value (current or future).