I've tried dozens of this type of tools over the years, most in the past ten years as we got ready to retire and then retired a few years ago. Many of the tools were simplistic like Fortunately, but some give better information like I-ORP, On Trajectory, Pralana, Flexible Retirement Planner, ESPlanner and the Bogleheads Retiree Portfolio Model. See the BogleHeads Wiki page on retirement calculators [0] for a bigger list and links to these tools. Darrow [1] also has good reviews of retirement calculators.

Fortunately in its current state doesn't help me at all. It wouldn't have helped me 10 years before retirement either.

You probably want to join the BogleHeads forum [2], as many of these folks could be your potential customers, but they are also your competition that gives away excellent advice for free. Look at the questions that are asked and the high quality answers and see if you can replicate them in your tool.

Claims from the FAQ page:

- Takes into account capital gains. But it didn't ask any basis information about my brokerage balance. Does it guess? What value did it use?

- Takes into account income tax. It didn't ask my breakdown of stocks/bonds in the brokerage account or in my retirement accounts. How are dividends and interest handled?

- Social Security needs to be modeled. The free open source tools at https://ssa.tools and https://opensocialsecurity.com contain the minimum that you need to model. The question "Should I work one more year?" is a common one and one you need to handle.

- Health care is not even on the list of things ignored and it's one of the biggest questions for folks retiring early. It has huge effects on federal taxes and the ACA cliff caused some folks to keep their income artificially low. IRMAA [3] is also a concern for some folks.

- There is no way to separate traditional retirement accounts from Roth type accounts which have very different tax treatments.

- A common question for early retirees is should I do a Roth conversion or should I take advantage of the 0% capital gains bracket? Modeling the RMDs and the taxes on that is complex, but absolutely necessary to properly answer this question.

- Ignoring state taxes can give misleading answers to some of the questions above. I live in a state that taxes capital gains as income, like many states. So when I take advantage of the 0% federal cap gains bracket, my state taxes can be 3-4x my federal taxes.

It looks like you are targeting younger customers that will have lots of uncertainty with how the market will go and what will happen with tax policy. Often times these customers are just as well served by the Mr Money Mustache savings curve [4] and low cost index investing.

I think the real opportunity to make money is helping with the hard problems of folks about to retire and those that are retired. Tools like RPM are difficult to use. A web tool that uses an interview process to collect the data and then writes out a spreadsheet might be a useful tool.

[0] https://www.bogleheads.org/wiki/Retirement_calculators_and_s...

[1] https://www.caniretireyet.com/the-best-retirement-calculator...

[2] https://www.bogleheads.org

[3] https://thefinancebuff.com/medicare-irmaa-income-brackets.ht...

[4] https://www.mrmoneymustache.com/2012/01/13/the-shockingly-si...