💰 Expense Tracking & Budget Control System

1. Purpose

Companies need a simple way to track employee expenses, set yearly spending budgets for each expense category, and get alerts before they overspend. This system serves multiple organisations at once — each organisation gets its own private workspace where only their team can see their data.

• Each organisation signs up and chooses a subscription plan.
• The organisation admin invites team members and assigns them roles.
• Team members record their expenses under named categories.
• The system monitors spending against the budget and sends alerts.
• Managers and Admins can view the full team's monthly spending report.

What Makes It Multi-Tenant?

A single running application serves many organisations at the same time. Each organisation's expense data, categories, budgets, and users are completely private. One company cannot see another company's data — even though they are all using the same system.

2. Business Scenario

TechCorp BD is a software company with 8 employees. The company owner, Rahim Ahmed, signs up for the platform, chooses the Pro Plan, and creates the company workspace. He sets up five expense categories and a yearly budget for each. He then invites his team — some as regular Members who add their own expenses, and one senior as a Manager who can review the team's full spending.

Every time a team member spends money — a taxi ride, a team lunch, a software subscription — they open the app and record the expense. The system checks if the spending is close to or over the budget, and alerts the Admin and Manager if needed. At the end of each month, the Manager opens the Monthly Summary to see how much each category has been spent, and whether the team is on track.

Daily Operations

Expense Categories (TechCorp BD)

Soft Limit vs Hard Limit

3. Users & Roles

The system has four types of users. Each organisation has its own set of users, separate from all other organisations.

4. Subscription Plans

Each organisation chooses a plan when they sign up. The plan determines how many users they can invite, how many expense categories they can create, and how far back they can see their history.

Plan Limits Enforced by the System

• If an organisation is on the Starter plan and already has 3 users, inviting a 4th user is blocked — the system shows an upgrade prompt.
• If a Starter organisation tries to create an 11th expense category, the system blocks it and suggests upgrading.
• Starter organisations cannot see expense history older than 6 months. The data is kept, just hidden until they upgrade.
• An organisation cannot downgrade to a lower plan if their current usage exceeds that plan's limits.

5. Core Features

MVP Features (Build These First)

• Organisation sign-up and workspace creation
• User invitation with role assignment
• Login with organisation context
• Create and manage expense categories
• Add and view expenses (members see only their own)
• Set yearly budget per category (Soft Limit only)
• In-app budget alert at 80% threshold
• Monthly summary screen (Managers and Admins only)
• Platform dashboard for Super Admin (organisation list)

6. Main Screens — UI Mocks

7. System Flows

Flow 1: Organisation Sign Up

Flow 2: Add an Expense (Member)

Flow 3: Over-Budget Approval (Manager)

Flow 4: Invite a Team Member (Admin)

Cancellation / Correction Flow

8. Important Business Rules

Expense Entry Rules

• An expense amount must always be positive. Zero or negative amounts cannot be saved.
• An expense date cannot be set to a future date.
• Every expense must have a category. A category cannot be left blank.
• If the same date, amount, category, and description already exist, the system warns the user — but does not block them.
• A member can only edit or delete their own expenses, and only if they belong to the current year. Previous-year expenses are locked.
• Corrections and refunds must be entered as Adjustment Entries. The original expense is never modified.

Budget Rules

• Only one budget can be set per category per year, per organisation.
• If no budget is set for a category, spending is treated as Unlimited — no alerts will fire.
• Only the Tenant Admin can set or change a budget. Only the current year's budget can be changed.
• Budget amounts can include decimals (e.g. ৳15,000.50).

Expense Category Rules

• Category names must be unique within the same organisation (not case-sensitive — "Travel" and "travel" count as the same).
• A category name cannot be blank or contain only spaces. Maximum 50 characters.
• Only the Admin can create, edit, or deactivate categories.
• Deactivating a category hides it from the expense entry screen, but all past expenses recorded under it remain visible in reports.
• A deactivated category can be reactivated at any time.
• Starter plan organisations cannot create more than 10 categories. Creating an 11th is blocked until they upgrade.

Overspending Rules

• When spending reaches 80% of the budget, the system sends an alert. This alert fires only once per month per category.
• Soft Limit: The expense is saved and marked "Over Budget". An alert is sent to Admins and Managers.
• Hard Limit: The expense cannot be saved without Manager or Admin approval. The entry waits in "Pending" state.
• An approved Hard Limit entry is saved with a note of who approved it and when.
• A rejected Hard Limit entry is permanently discarded. The member is told the reason.

Organisation & Workspace Rules

• Each organisation's data is completely private. One organisation cannot see another's expenses, categories, or budgets.
• Only the Tenant Admin can invite users, change roles, or remove members.
• When a member is removed from an organisation, their past expense entries remain in the organisation's records.
• A member can belong to multiple organisations and will see a workspace selector after logging in.
• Invitation links expire after 48 hours. If not accepted, the Admin must resend.

Notification Rules

• In-app notifications are on by default for all users.
• Email and SMS alerts are available on Pro and Enterprise plans only.
• Notifications for the same event (e.g. 80% alert for the same category) are sent only once per period to avoid spam.
• Approval request notifications are sent immediately to all Managers and Admins in the organisation.

9. Example Report Data

Monthly Summary Report — TechCorp BD, June 2026

Member-Wise Spending — June 2026 (Manager View)

Super Admin — Platform Overview

10. Technical Specification

You can use any programming language you want.

You can use any database — or even an in-memory data store for the first version.

The project can be a console, desktop, or web application.

Focus on the object design: how are Organisations, Users, Expense Categories, Expenses, and Budgets represented as classes, and how do the business rules connect them?

11. Advanced Topics — For Discussion

The three questions below are not part of the MVP. They are discussion topics for when the system grows into a large-scale SaaS product serving thousands of organisations and millions of daily expense entries. Think about them from a business and product perspective — not just a technical one.