---
title: "Hold money as integer minor units · Agent Wranglers"
url: https://agentwranglers.se/playbook/payments/amounts-and-orders/money-in-minor-units
updated: 2026-10-20
licence: "All rights reserved"
---

# Hold money as integer minor units everywhere

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Required
- Chapter: [Amounts and orders](https://agentwranglers.se/playbook/payments/amounts-and-orders)
- Rule: Hold every amount as an integer count of the currency's minor unit, with its ISO 4217 code, in code, database, provider calls and stored events.
- How: The API rule [money](https://agentwranglers.se/playbook/api-design/requests-and-responses/money) sets the wire format, and [exact types](https://agentwranglers.se/playbook/data/schema-design/exact-types) sets the column type. Inside the code, use one money type that carries amount and currency, as in [value objects](https://agentwranglers.se/playbook/architecture/data-shapes/value-objects). Refuse to add amounts in two currencies. Look up each currency's number of decimals, since JPY has none and KWD has three. Some providers differ from ISO 4217 for a few currencies, so convert through one tested function. Format for display only at the edge, in the reader's locale.
- Check: A unit test adds SEK to EUR and expects an error. Search the payment code for `parseFloat`, `float(` and `Number(` applied to amounts. Nothing is found.

Example:

```js
class Money {
  constructor(minor, currency) {
    if (!Number.isSafeInteger(minor)) throw new TypeError('Amount must be a whole number of minor units')
    Object.assign(this, { minor, currency })
    Object.freeze(this)
  }
  plus(other) {
    if (other.currency !== this.currency) throw new Error(`Cannot add ${other.currency} to ${this.currency}`)
    return new Money(this.minor + other.minor, this.currency)
  }
}
```

```python
from dataclasses import dataclass

@dataclass(frozen=True)
class Money:
    minor: int
    currency: str

    def __add__(self, other: "Money") -> "Money":
        if other.currency != self.currency:
            raise ValueError(f"Cannot add {other.currency} to {self.currency}")
        return Money(self.minor + other.minor, self.currency)
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers payments playbook: https://agentwranglers.se/playbook/payments/amounts-and-orders/money-in-minor-units`.

- Next: [Split amounts without losing a cent](https://agentwranglers.se/playbook/payments/amounts-and-orders/allocate-remainders)
- [Amounts and orders](https://agentwranglers.se/playbook/payments/amounts-and-orders)