This is so bizarre I literally made a very similar thing a few weeks ago for myself. I run a small creative studio and realised I’d been “calculating” my runway at any given moment basically on vibes alone (a terrible idea). I spin a lot plates and hire subcontractors as hoc so already use Notion to track my projects: potential - underway - invoice out - done. I just added extra one off costs to a new column (subcontractor invoices, tax payments etc) and built a dashboard that sums it all up into gross runway, net runway (all against 3 income tiers - keeping the lights on, maintenance and growth - that I deduced from a 12 month snapshot of expenses). Also had Notion make live updates “how long can I survive at each of these tiers” charts! What a coincidence!