Q.What is Invoice?

The Source Document: Where Every Accounting Story Begins

Think about the last time you bought something from a shop. You paid, and the shopkeeper handed you a small slip of paper — a receipt. That receipt is proof that money changed hands. Without it, if you later claimed you paid and the shopkeeper said you didn't, you'd have no way to prove your side.

Now imagine a business. Every day, hundreds of transactions happen: goods are sold, salaries are paid, electricity bills are settled, raw materials are purchased. If the accountant simply remembers these transactions or writes them on scraps of paper, chaos follows. How do you know a payment was actually made? How do you prove to the tax department that an expense was genuine? How do you settle disputes with suppliers or customers?

This is where the source document enters the picture.

What Exactly Is a Source Document?

A source document is the original written evidence that a transaction has occurred. It is the first piece of paper (or digital record) that captures the financial event. In accounting, you never record a transaction without a source document to back it up.

Common examples include:

• Cash Memo – issued when goods are sold for cash
• Invoice (or Bill) – issued when goods are sold on credit
• Receipt – given when cash is received
• Debit Note – sent when goods are returned to a supplier (or when the supplier has overcharged)
• Credit Note – sent when a customer returns goods (or when you have overcharged the customer)
• Pay Slip – evidence of salary paid to an employee
• Bank Statement – evidence of bank transactions
• Cheque Book Counterfoil – proof that a cheque was issued

Each of these documents carries specific details: date, amount, parties involved, nature of transaction, and often signatures or stamps.

Why Does It Matter So Much?

Here is why source documents are non-negotiable:

1. Authenticity and Proof – A source document is legal evidence. If the tax department audits the business, every expense claimed must be backed by a valid bill. Without it, the expense is disallowed and the business pays extra tax.

2. Accuracy – The accountant records exactly what the source document says. This prevents errors from memory or guesswork.

3. Verification – When two sets of books are compared (e.g., the buyer's and seller's records), source documents are the common reference point. Discrepancies are spotted quickly.

4. Audit Trail – An auditor can trace any entry in the ledger back to its source document. This is the backbone of accountability.

5. Legal Compliance – Under the Goods and Services Tax (GST) regime in India, every registered business must issue tax invoices. Failing to maintain proper source documents can lead to penalties.

The Accounting Treatment: How Source Documents Drive the Journal Entry

Every source document tells the accountant two things: which account to debit and which account to credit. The accountant reads the document, applies the rules of debit and credit, and records the transaction in the journal.

Let us walk through a concrete example.

Example: Goods Sold for Cash

Source Document: Cash Memo (issued by the seller)

Details on the Cash Memo:

• Date: 1st April 2025
• Sold to: Mr. Sharma
• Goods: 10 units of Product X @ ₹500 each
• Total: ₹5,000
• Cash received: ₹5,000

Accounting Treatment:

The business receives cash (asset increases → debit) and gives away goods (revenue earned → credit).

The narration at the end explicitly mentions the source document — "as per Cash Memo No. 101". This is standard practice.

Example: Goods Purchased on Credit

Source Document: Invoice (received from the supplier)

Details on the Invoice:

• Date: 2nd April 2025
• Supplier: M/s Gupta Traders
• Goods: 20 units of Raw Material Y @ ₹200 each
• Total: ₹4,000
• Credit terms: Payment due in 30 days

Accounting Treatment:

The business receives goods (asset increases → debit) and creates a liability to pay later (liability increases → credit).

A Special Case: Interest on Capital

When the owner brings capital into the business, the business may pay interest on that capital. This is a common adjustment in partnership accounts (Class 12 syllabus).

Source Document: A Debit Note or an internal memorandum (since the business is paying interest to the owner, there is no external party issuing a bill — the firm creates its own document).

Formula for Interest on Capital:

Interest on Capital = Capital × Rate of Interest × Time Period

For example, if a partner has contributed ₹1,00,000 as capital and the partnership deed allows interest at 10% per annum for one year:

Interest = ₹1,00,000 × 10/100 × 1 = ₹10,000

Accounting Treatment: …