# Day count & proration

> 30/360 is wrong about the calendar and right about the contract. Both are here.

Source: https://lopifi.com/tools/daycount
Part of: Lopifi — US GAAP books on autopilot, reviewed by a CPA (https://lopifi.com)

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- **Group:** Dates

## Inputs

- `start` — From
- `end` — To
- `annual` — Annual amount to prorate
- `currency` — Currency (ISO 4217 code — sets the decimals: JPY 0, USD 2, KWD 3.)

Runs entirely in the browser: no network call, no data leaves the page. The same definition powers the Lopifi Tools Chrome extension.