In more detail
A good invoice has a unique, sequential number, the date of issue, both parties' names and addresses (and tax numbers where required), itemised lines with quantities and prices, any tax shown separately, the total, and payment terms. "Net 30" means payment is due 30 days after the invoice date; "2/10 net 30" offers a 2% discount for paying within 10 days. In VAT systems the invoice is the document that lets a business buyer reclaim the VAT it paid. Legal requirements vary by country.
Why it matters
A vague or incomplete invoice is the most common reason payments are late or rejected by a client's accounts department. Clear terms also set the date from which late fees or interest can be claimed.
Example
Invoice no. 2026-0142
Issue date 2026-10-09
Due date 2026-11-08 (net 30)
Web design 3 days x $450.00 $1,350.00
Hosting setup 2.5 h x $120.00 $300.00
Subtotal $1,650.00
VAT 20% $330.00
Total due $1,980.00
Skipping a 2/10 net 30 discount to pay 20 days later is like borrowing at 2/98 × 365/20 = 37.24% a year, so taking the discount usually pays.