Integer Paisa & Money Math

One of the most frequent sources of payment bugs and silent reconciliation failures in fintech applications is floating-point arithmetic drift (e.g. 0.1 + 0.2 === 0.30000000000000004).

To make nepay mathematically deterministic and safe across all databases and platforms, every monetary amount in the public API is an integer paisa.

The Paisa Rule

1 NPR (Rupee) = 100 Paisa

Every amount passed to initiatePayment() or returned by verifyPayment() is represented in integer paisa. Never pass decimal amounts or floating-point numbers.

NPR Display	Paisa Value	Note
NPR 10.00	1000	Minimum allowed transaction for Khalti
NPR 50.50	5050	Fractional rupee
NPR 100.00	10000	Standard test transaction
NPR 1,250.75	125075	No commas, pure integer

Built-in Conversion Helpers

The SDK provides three dedicated helpers for converting between rupees and paisa:

import { nprToPaisa, paisaToRupeesString, parseAmountToPaisa } from "@bivekkk/nepay";

1. nprToPaisa(npr: number): number

Converts a decimal rupee number to integer paisa using Math.round(npr * 100).

nprToPaisa(123.45); // => 12345
nprToPaisa(10);     // => 1000

2. paisaToRupeesString(paisa: number): string

Converts integer paisa into a formatted decimal string (up to 2 decimals) required by gateways such as eSewa’s form inputs.

paisaToRupeesString(12345); // => "123.45"
paisaToRupeesString(10000); // => "100" (trailing zeros trimmed)
paisaToRupeesString(10050); // => "100.5"

3. parseAmountToPaisa(raw: string | number): number

Strips commas and formatting quirks from callback responses and parses them back into safe integer paisa.

parseAmountToPaisa("1,000.0"); // => 100000
parseAmountToPaisa("1250.50"); // => 125050
parseAmountToPaisa(100);       // => 10000

Why This Matters in Gateway Communication

eSewa (ePay v2)

eSewa requires decimal rupees in form submissions (e.g. "100" or "112.50"). When eSewa redirects back to your callback, it often formats amounts with commas:

{
  "total_amount": "1,000.0"
}

If you perform string equality total_amount === "1000", the verification would fail! nepay solves this by:

1. Verifying the HMAC-SHA256 signature against the raw string as received ("1,000.0").
2. Stripping commas and parsing the amount to paisa (100000) for exact numeric comparison against expectedAmountPaisa.
3. Normalizing to plain decimal "1000.0" before invoking eSewa’s status query endpoint.

Khalti (ePayment v2)

Khalti operates natively in integer paisa:

• Minimum amount is 1000 (NPR 10). Passing less throws a pre-flight validation error.
• Breakdown sum (amount_breakdown[].amount) must equal amount in paisa.