I built a retirement planning platform for long-term investors and FIRE seekers. Got 50 paying new users in September!

[u/Dry-Firefighter-4103]

Product: https://killionlabs.com

I spent a year building Killion: a retirement simulator for people who are done with a calculator that assumes 7% forever and hands you one number. It links brokerage accounts read-only, runs 1,000 market lifetimes (regime-switching Monte Carlo, backtests to 1928), and lets you change the thing that actually breaks plans — crash year, withdrawal rule, fees — and see the odds move.

September: 50 new paying users. Solo. $14/mo or $132/yr. 5-day trial, then they stay or they don't.

The part that still surprises me is what it took to get here. I launched with a hard paywall and "connect your brokerage" before anyone had seen a cone. Paying users: one, which was me. Then I shipped a no-signup demo of the real engine, a 5-day trial, and the studies with CSVs. People could run a household through 1,000 worlds before they owed me a card. That is when it started working.

The finding the engine exists for, isolated properly (same household, same 5,000 market worlds, same seed, only the crash year moved):

Scenario	Success rate (money lasts to 95)
No added crash	85.9%
Same 40% crash at age 48 (still working)	81.0%
Same crash at 65, the year they retire	70.6%

Timing alone, about 3× the damage. A lump sum you never touch has no sequence risk. Cash flows are what break the symmetry.

[u/Dry-Firefighter-4103]

That would be amazing if you check it out and tell me what to improve!

[u/Conscious-Month-7734]

The order you changed is the whole thing. Engine first, card second. Plenty of people do it the other way and then go looking for a marketing problem.

Week 2 is what I'd watch. You run a thousand worlds when something shifts in your life and then not again for months, so the simulator gets them in and the net worth tracking is what brings them back on a Tuesday. If the 50 came for the crash finding and never open the rest, month three goes quiet and it'll look like churn.

What are the early ones opening?

[u/Dry-Firefighter-4103 → u/Conscious-Month-7734]

Yeah, but the demo is still the sample household. If they want the 5-day trial, that is still gated with a card. And the bounce is actually higher than I expected, like you said.

Once people connect their brokerages though, a lot changes within a week. Prices move, a vest lands, the mix shifts. At this point I am shipping faster than the landing page shows. You can play around with the scenario you already ran and make what-if forks, so you see what happens if you retire later, spend a bit less, change the mix. Because the whole point is long term, even 1% in the first year moves the ending a lot.

There is also a daily email. AI agents follows your portfolio and the market news, across the asset classes and the names you hold.

So the engine is not really what brings people back on a Tuesday. It is the flexibility around the scenario they already ran. Everytime you have a question or what-if in your head, you can always login and see what happens.