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📈 Simple Interest Calculator Overdue invoices & payment plans

Estimate interest on client invoices

Use this free simple interest calculator to understand how much interest you might charge on overdue invoices or long-term payment plans.

Calculate simple interest & total payable

Based on the classic formula: Principal × Rate × Time / 100.

Interest amount: - · Total payable: -

This is a simple-interest estimate. Real contracts and local regulations may differ—always double check before finalising.