Proforma Invoice Methodology — Complete Guide

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CalculatorAI's reference for writing professional proforma invoices that satisfy customs brokers, banks, and corporate buyers. Every section covers what to include, why it matters, and standard trade guidelines. Used as the public guide AND as background context for the editor's AI Help mode.

What is a proforma invoice (and what it isn't)

A proforma invoice is a preliminary bill of sale sent to buyers in advance of a shipment or delivery of goods. It acts as a draft invoice that details the items, quantities, value, and transport charges, and is highly critical for international trade.

Key document distinctions:

• Proforma Invoice: Sent before delivery. It is a quote formatted as an invoice, detailing the seller's commitment to ship specified items. It has no accounting status and cannot be booked to a ledger.
• Commercial Invoice: Sent after delivery or shipment. It is the final legal request for payment, triggers tax liabilities (VAT/GST), and is booked as an actual account receivable.
• Purchase Order (PO): Sent by the buyer to the seller to request/authorize the purchase of goods.

Required fields & what each one is for

A proforma invoice must look extremely similar to a standard invoice, but with key differences:

"PROFORMA INVOICE" header. Must be boldly printed at the top. Tax authorities and customs agents inspect headers closely to ensure a business is not using draft proforma invoices to bypass sales tax or book unofficial revenues.

Issuer & Customer blocks. Identifies the legal entities. In international shipments, include detailed contact details (phone, email) for both customs agents to query.

Proforma Number. Unlike commercial invoices, sequential gap-free numbering is not strictly demanded by tax law for proformas, but using a tracking series (e.g. PRO-2026-004) keeps your shipping records organized.

Detailed descriptions & HS Codes. For customs clearance, each line item must have its Harmonized System (HS) Code and country of origin to determine duty rates.

Customs usage & global shipping

In cross-border logistics, proforma invoices are primary documents used to declare the estimated value of goods for:

• Duty assessment: Customs officers use the declared value on the proforma to calculate import taxes.
• Import licenses: Many countries require an approved proforma to grant import permits before shipping.
• Letters of Credit: Banks require proforma invoices to release advance funding and secure financing.

Digital Signatures (Signature Canvas)

To speed up document authorization and present a professional brand identity, the CalculatorAI editor includes an interactive Signature Canvas drawing pad.

• Drawing a Signature: Click the "Show Signature" checkbox in the settings drawer on the right sidebar. Under the notes/terms area in the template preview, a dashed placeholder block will appear. Click it (or click "Draw Signature" in the right sidebar) to open a signature pad modal. You can draw your signature using a mouse, trackpad, or touch screen.
• Privacy-First Storage: Storing handwritten signatures can be a privacy concern. CalculatorAI stores your drawn signature locally as a base64-encoded PNG data URL directly inside your document draft's JSON structure. It is never uploaded to public folders or shared asset servers, ensuring your signature remains strictly private.
• PDF Rendering: Once saved, the signature is rendered at the bottom of the document preview and automatically embedded into all 5 PDF themes during download.