Free Business Billing Calculators

Six free calculators for the financial math behind small business billing: late payment fees and interest, sales tax, business expense deductions, subscription revenue (MRR), loan and installment amortization, and cash flow projections.

What can you calculate?

Work out interest on overdue invoices, add or back out sales tax from any amount, estimate deductible business expenses, model recurring subscription revenue and churn, build installment repayment schedules, and project cash flow over rolling weekly or monthly periods.

Frequently Asked Questions

Are the calculators free?

Yes. All calculators are free with no signup and run entirely in your browser.

Can I save my calculations?

Results can be used directly in the document generators — for example, applying a late fee calculation to a past-due notice.