Most retirement calculators are US-bound templates with a rupee symbol. DhanPlan treats Indian instruments — SIP, EPF, PPF, NPS, FIRE — as first-class columns, each with institutional-grade assumptions. It taught me that scope discipline and honest model math beat feature ceilings.
Building a financial product is a product where the model is the product. DhanPlan started as a personal irritation: every calculator I tried asked for a 401k. India's mental math is not that.
The scope decision
We shipped four modules before adding anything else:
- SIP — equity growth with inflation-adjusted terms
- EPF & PPF — the two most Indian fixed instruments, with their year caps and growth floors
- NPS — the worker's savings-with-tax angle
- FIRE — the retirement milestone everyone in 2026 asks for
Each module gets its own projection logic; the UI is honest that no model predicts a market.
What made it ship
The scoping rule was: a feature must be defensible by two public data points. If we couldn't cite the instrument's mechanics, it didn't ship. This killed feature-creep in week one.
What the product taught me
- Model quality over field count. Four truthful modules out-rank twenty wish-list fields.
- Tests are part of the product. Breakage here loses trust along with money.
- The boring math is the feature. A user who can't reconcile a number won't come back.
What I'd do differently
- Let the modules export a plan (CSV/JSON) before inviting login walls — export early, gate later.
- Carve the inflation story harder. Users mentally undercount inflation; surfacing each row's real-growth number is the retention wedge.
DhanPlan lives on the projects page. For the product-method side, data decisioning and scope from discovery are the PM muscle this product practices.