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
Mortgage Calculator Pro
Featured by Apple in "What's Hot" List
$0.99 · In-app purchases
PRICE
$0.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.3
72 ratings · Top 30%
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 included16 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 Mortgage Calculator Pro: map the core Finance workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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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
Add features like extra payment calculators or investment comparisons
Assumption to check: Limited functionality for advanced users
Validate with people who use this workflow before building.
Hypothesis 2
Implement clearer purchase flow and trial options
Assumption to check: In-app purchase confusion
Validate with people who use this workflow before building.
Hypothesis 3
Include educational content about mortgages and interest rates
Assumption to check: Lack of financial education resources
Validate with people who use this workflow before building.
Hypothesis 4
Implement a modern design with improved UX/UI principles
Assumption to check: User interface feels outdated
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
Featured by Apple in "What's Hot" List Mortgage Calculator Pro is a quick and easy to use calculator for brokers, realtors, and home buyers. Within seconds, you will be able to calculate the monthly payment for a mortgage, car payment, credit card, or other types of fixed rate loans. The calculator lets you add different adjustments such as insurance, property tax, and monthly fees such as HOA to see of they would affect the monthly payment. FEATURES * Optimized for Multitasking and Retina Display - Supports fast app switching and higher resolution Retina display. * Ability to Save Loans - Mortgage Calculator Pro lets you save and organize all your various loans in the Favorites list so you do not have to enter the information over each time. It will also remember and opens up the last saved loan you worked on. * Large Numeric Keypad - The large keypad allows for easier, faster, and more accurate entry of numeric amounts. * Email Quote - Send loan information and amortization schedule via email. * Fast Calculations - Mortgage Calculator Pro is designed to be fast. Calculations are done instantly after you enter each amount field. * Amortization Table - A complete payment schedule allows you to view the interest, principal, and remaining balance for each and every payment of the loan. * Backup / Restore - Backup your data to your computer for safekeeping. Then restore it to your iOS device when you need to via the iTunes file sharing interface. * Other Features - Ability to specify length of loan in months as well as years, allow up to three decimal places for the interest rate field, switch to loan calculator view when a saved loan is selected, price per square foot calculation, down payment and annual tax calculation based on percent or manual entry, and much more to come. * Intuitive User Interface - Special attention was given to the user interface to ensure that it is clean, intuitive, and easy to use.
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
React Navigation
React Native Paper
Zustand
BUILD KIT DIFFICULTY
Starter
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.
