Send a clear quote with a validity date, then turn it into an invoice with one click when the client says yes.
Quotes use their own numbering series (for example Q2026-001), have a “valid until” date, and can be marked accepted or declined. When a quote is accepted, choose More → Convert to invoice and every line, discount and client detail is carried over to a new invoice draft.
An estimate is an approximate price; a quote is a fixed offer. Use the quote for both, and say in the notes whether the prices are fixed or an estimate.
There is no account and no server behind this invoice generator. Your business details, clients, products and invoices are stored in your browser's own database (IndexedDB) and never uploaded. The PDF is built on your device. The only request the app ever makes on its own is optional: if you click Use ECB rate on a foreign-currency invoice, it asks the European Central Bank for that day's reference rate — sending just the two currency codes and the date. That also means nobody else has a copy — download a backup from Settings → Backup now and then, and keep it with your accounting files. Nothing is locked in: every PDF carries its own data, the backup format is documented, and you can download an offline copy of the whole app.
It is good practice to show prices the same way the invoice will, including tax, so the client knows the final amount.
The quote is kept as it was and marked as invoiced. The invoice is a new draft you can still edit before issuing.