Invoice Calculator
Total an invoice from line items, a discount and a tax rate — with the subtotal, discount, tax and grand total broken out.
How it works
Subtotal = Σ(quantity × unit price) · Total = (subtotal − discount) × (1 + tax%)
Each line item is quantity times unit price; the subtotal adds them up. Any percentage discount is taken off the subtotal first, and tax is then charged on the discounted amount — the usual order, since customers are taxed on what they actually pay. The grand total is the discounted subtotal plus tax.
Worked example
Two line items — 10 × $50 and 5 × $120 — subtotal to $1,100. With no discount and 8% tax ($88), the invoice total is $1,188.
Frequently asked questions
Is tax applied before or after the discount?
This calculator applies the discount first, then charges tax on the reduced amount — the usual approach, since customers are taxed on what they actually pay. Local rules can vary.
Can I add more than three line items?
This tool totals up to three lines for a quick estimate. For a full invoice with many items, dedicated invoicing software handles line items, tax and totals automatically.
Does this handle multiple tax rates?
No — it applies one rate to the whole invoice. If different items carry different tax rates, calculate each group separately and add the totals.
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Educational estimate, not financial advice.