Invoice Late Fee Calculator. Calculate late fees on overdue invoices from the amount, monthly rate, payment terms and days elapsed. Free tool, no signup. Work out what an overdue invoice actually owes you. Built for small business owners who want a simple, free toolkit to run inventory, send invoices, manage customers, track suppliers, and understand sales without paying for bloated enterprise software. ExpressBizTools runs in your browser, works on phones, tablets, and laptops, and never charges per user. Create invoices in seconds, scan barcodes with your phone camera, watch low-stock alerts so you never lose a sale, and export clean reports when it is time to file taxes or talk to your accountant. Whether you run a retail shop, a freelance practice, a restaurant, a salon, an Etsy store, a food truck, or an auto repair shop, the same workflow handles your day-to-day. No signup is required to try it, and your data stays yours.