Build PHP Invoice Tracker

I need a small web application built in PHP and MySQL to manage invoices and expenses for a freelance business.

Right now everything is in Excel, and I want to replace it with a simple system that is easier to use and gives a clear overview of income, expenses, and unpaid invoices.

This should be a basic, clean solution. No frameworks or overly complex setup.


Main Requirements:

Login system (single user, no registration)
Client management (add, edit, delete)
Create invoices with multiple items (description, price, quantity)
Automatic total calculation
Mark invoices as paid/unpaid
Add and manage expenses
Simple dashboard showing:
total income
total expenses
net profit
unpaid invoices
Printable invoice page (browser print is enough)