I made a spreadsheet where formulas also update backwards
Details
- External ID
- 46234734
- Source
- HN
- Company
- —
- Product
- I made a spreadsheet where formulas also update backwards
- Website domain
- github.io
- Launched
- Dec. 11, 2025
- Cohort
- —
- Upvotes
- 252
- Upvotes percentile
- 0.9618320610687023
- Tags
- —
- Fetched at
- Sept. 7, 2026, 9:25 p.m.
- Updated at
- Sept. 7, 2026, 9:25 p.m.
Description
Hello HN! I'm happy to release this project today. It's a bidirectional calculator (hence the name bidicalc).I've been obsessed with the idea of making a spreadsheet where you can update both inputs and outputs, instead of regular spreadsheets where you can only update inputs.Please let me know what you think! Especially if you find bugs or good example use cases.
Enrichment
- Theme
- calculators and financial estimation tools
- Vertical
- Horizontal
- Function
- Dev tools
- Audience
- Prosumer
- AI stance
- Not AI
- Project type
- Hobby / open-source project
- Normalized one-liner
- spreadsheet with bidirectional formula updates
- Manually corrected
- False
Could you build this?
Partial Building a reactive spreadsheet grid UI is straightforward, but solving non-linear, multi-variable systems backward requires integrating or implementing robust constraint satisfaction/numerical solver algorithms.
What it would actually take: The core engine needs an AST parser for spreadsheet formulas coupled with a numerical equation solver or constraint satisfaction system (such as Levenberg-Marquardt, gradient descent, or an SMT/Z3 solver) with heuristics to resolve under-determined systems. Specialized knowledge of numerical analysis and algorithmic constraint programming is required.
Discussion
20 comments analyzed.
Competitors mentioned: Excel Solver, Prolog constraint logic programming, Autodesk Fusion 360 sketcher, DOS-era "crooked accountant's spreadsheet"
Concerns raised: Solver fails on certain exact target values (e.g., A3=100 doesn't work but 99/101 do), Cannot simultaneously fix multiple output values, Degrees of freedom ambiguity makes behavior unpredictable, Spooky action at a distance UX confusion
Feature requests: Support for multiple simultaneous output targets, Visual indication of constrained vs free cells (like Fusion 360's blue/black coloring), Default to fixed cells unless explicitly marked as solver variables, Visualization showing which cells will move when editing one, VLOOKUP support
Competitors
Other products that read as similar to this one — 35 launches clear the similarity bar, closest 8 shown.
Attention rank: #3 of 36 (itself plus its competitors, highest first — normalized so YC and Product Hunt are compared fairly).
Launched 41 days after the earliest competitor.
- Pane · hn · 2026-01-12 · 32 upvotes · similarity 0.40
- calc · ph · 2026-09-30 · 1 upvotes · similarity 0.38
- Calculaxy · ph · 2026-09-20 · 1 upvotes · similarity 0.37
- I made a calculator that works over disjoint sets of intervals · hn · 2026-04-18 · 314 upvotes · similarity 0.37
- XanCalc · ph · 2026-09-18 · 1 upvotes · similarity 0.36
- Calculator · ph · 2026-09-07 · 1 upvotes · similarity 0.35
- SpreadIntel · ph · 2026-09-22 · 2 upvotes · similarity 0.34
- Clear Calc - Native Calculator · ph · 2026-09-10 · 2 upvotes · similarity 0.34
Other launches for this product
- No other launches for this product.
Same idea, different domain
Nobody's really built a dev tools tool for Sales yet.