Invoice Calculator

Accurate billing depends on getting every total right for the goods or services you delivered. With the average small business sending invoices 2.7 times per week in 2026, handling line items, tax (say a 7.5% state sales tax), discounts, and payment terms cleanly is what keeps cash flow steady and client relationships intact.

Calculation runs in a set order. Each Line Item Total comes from Quantity times Unit Price, and those totals are summed into a subtotal. Any Discount, whether a percentage or a fixed amount, applies to that subtotal next. Tax is then figured on the discounted subtotal, or on the pre-discount subtotal where jurisdiction or preference dictates, and added together with any Shipping/Handling fees to reach the Grand Total Due.

Verify the tax rate every time, since rates swing widely by state and locality in 2026; California's statewide sales tax is 7.25%, yet local additions routinely push the effective rate higher. Applying a discount on the wrong side of tax is an easy slip that leads to under- or overcharging. State payment terms plainly as well, such as Net 30 or Due on Receipt, to head off delays in collection.