Calculate the days sales in inventory ratio, an efficiency ratio that measures how long it takes a company to sell its inventory.

The days sales in inventory ratio (DSI) is calculated by dividing the average inventory by the cost of goods sold (COGS) and then multiplying by the number of days in the period. It represents the average number of days it takes for a company to sell its inventory. A lower DSI indicates that the company is selling its inventory more quickly.

The formula is as follows:

\[\text{Days Sales in Inventory Ratio} = (\text{Average Inventory} / \text{Cost of Goods Sold}) \cdot \text{Days}\]

Also known as: DIO, days inventory outstanding.

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Calculate the Days of Inventory Outstanding in Python

The Days of Inventory Outstanding is available in the Ratios module of the open-source Finance Toolkit. Install it with:

pip install financetoolkit -U

Then call get_days_of_inventory_outstanding as shown below.

from financetoolkit import Toolkit

toolkit = Toolkit(["AAPL", "TSLA"], api_key="FINANCIAL_MODELING_PREP_KEY")

toolkit.ratios.get_days_of_inventory_outstanding()

Which returns:

  2021 2022 2023 2024 2025
AAPL 9.1181 9.4097 9.6109 11.814 10.7405
TSLA 44.7344 55.9945 61.0502 58.3231 57.307

Parameters

get_days_of_inventory_outstanding accepts the following parameters:

  • days (int, optional): The number of days to use for the calculation. Defaults to 365.
  • rounding (int, optional): The number of decimals to round the results to. Defaults to 4.
  • growth (bool, optional): Whether to calculate the growth of the ratios. Defaults to False.
  • lag (int | str, optional): The lag to use for the growth calculation. Defaults to 1.
  • standardize (bool, optional): Whether to standardize (Z-Score) the result. When combined with growth=True, standardizes the growth values instead of the raw values. Defaults to False.
  • trailing (int): Defines whether to select a trailing period. E.g. when selecting 4 with quarterly data, the TTM is calculated.
Asset Turnover Ratio Inventory Turnover Ratio Days of Sales Outstanding Operating Cycle Accounts Payables Turnover Ratio Days of Accounts Payable Outstanding Cash Conversion Cycle Cash Conversion Efficiency Receivables Turnover SGA to Revenue Ratio Fixed Asset Turnover Operating Ratio

The Ratios module page introduces the module, and the sidebar lists all of its functions.

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