What Is a Source Document in Accounting?

A source document in accounting serves as the original record of any financial transaction a business undertakes. This document captures the fundamental details of an economic event. It provides the foundational data from which all subsequent accounting entries are derived and recorded.

Why Source Documents Matter

Source documents provide concrete evidence that a transaction occurred, verifying the accuracy of financial records and ensuring reliability. These documents create a clear audit trail, allowing internal staff or external auditors to trace any financial entry back to its origin. This traceability is fundamental for maintaining transparency and accountability within a business’s financial operations.

Businesses must comply with various legal and regulatory record-keeping requirements, and source documents are central to meeting these obligations. The Internal Revenue Service (IRS), for example, requires businesses to keep records that support income, deductions, and credits, typically for at least three years from the date a tax return was filed. For employment taxes, records must be kept for a minimum of four years after the tax is due or paid, whichever is later. Without proper source documents, businesses may face difficulties during tax audits, potentially leading to disallowed deductions, penalties, or additional taxes.

Essential Features of Source Documents

A valid source document must clearly state the date the transaction took place, its monetary value, and identify all parties involved, such as the buyer and seller.

A clear description of the transaction explains what occurred. Many source documents also include evidence of authorization, such as a signature or approval stamp. Collectively, these features ensure the document is complete and provides all necessary information for accurate record-keeping.

Types of Source Documents

Common types of source documents include:
Sales invoices: Created by a seller and issued to a buyer to record a credit sale of goods or services. These documents detail the items sold, quantities, prices, terms of payment, and the total amount due.
Purchase invoices: Received by a buyer from a seller for goods or services acquired on credit, outlining the buyer’s obligation to pay.
Receipts: Common source documents issued for cash payments received or made, serving as proof of payment.
Checks and their corresponding check stubs or electronic records document payments made from a bank account.
Bank statements: Issued periodically by financial institutions, summarize all transactions that have cleared a business’s bank account.
Payroll records, such as time cards and pay stubs, document employee hours worked, wages earned, deductions for taxes like Social Security and Medicare, and net pay. These records are essential for calculating and reporting employment taxes.
Credit memos: Documents issued by a seller to a buyer to reduce the amount the buyer owes, often due to returns, allowances, or errors in billing.
Debit memos: Issued by a buyer to a seller to request a reduction in the amount owed, perhaps for similar reasons.
Journal vouchers: Internal documents used to authorize and record non-routine accounting adjustments, such as correcting an error or recording depreciation, for which no external source document exists.

Using Source Documents in Accounting

Source documents form the foundation for recording all financial transactions in a business’s accounting records, such as journals and ledgers. When a transaction occurs, a source document is generated to capture its details. This document is then reviewed for accuracy and completeness before the information is formally entered into the accounting system.

Many businesses now utilize electronic systems and software to manage digital source documents, scanning physical documents or receiving them electronically. These digital copies are stored securely and can be easily retrieved for verification, audit purposes, or to support tax filings. The IRS allows for both physical and digital records, provided digital records are legible and accurate.