Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Financial Calculator
Financial Calculator is a simple, yet powerful and accurate intuitive calculator.
$5.99 · In-app purchases
PRICE
$5.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.8
6 ratings · Top 50%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
Preview a sample Build Kit No email needed
Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Financial Calculator: map the core Finance workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
Preview ready. Verify your email to reveal and copy the full prompt.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Integrate more complex calculations and features.
Assumption to check: Limited functionality compared to advanced financial applications
Validate with people who use this workflow before building.
Hypothesis 2
Enhance UI with modern design principles.
Assumption to check: User interface may feel outdated
Validate with people who use this workflow before building.
Hypothesis 3
Provide comprehensive tutorials and FAQs.
Assumption to check: Lack of detailed help resources
Validate with people who use this workflow before building.
Hypothesis 4
Clarify subscription tiers and provide trial options.
Assumption to check: In-app purchase model can be confusing
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
Financial Calculator is a simple, yet powerful and accurate intuitive calculator. Video tutorial: http://www.echoboom.com/financialcalculator/ Features: * Time value of money. * Growing annuities. * Calculates N, Interest, Present Value, PMT and Future Value of money. * Bond valuation. * Cash flow analysis in an intuitive interface. * Analyzes investments: Internal Rate of Return (IRR) and Net Present Value (NPV) * Amortization and Loans. Support for Canadian mortgages. * RPN support. * Near instantaneous calculations. -- Note: Please, write to my address under the 'help' section when you believe you found a bug. I do read every email and fix them as soon as possible. I also try to implement all feature requests. -- As for the bad reviews: Please, read the FAQ on the help section if you believe numbers are wrong. It's usually people missing something on the settings when using the financial calculator. All emails have been answered and explained and there has not been a wrong calculation since version 1.1. Please if your email was replied and solved, change the review since it makes it look bad for everybody else.
Written user reviews are not shown here. Check current App Store reviews >
Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
React Native
Expo
Supabase
axios
@react-navigation/native
expo-sqlite
BUILD KIT DIFFICULTY
Intermediate
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
