Market capitalization is one of the simplest ways to track how the market values a company over time. It changes as share price changes and, when relevant, as share count changes. For analysts and developers, historical market cap data is useful because it gives a clean company-size series without requiring every workflow to manually reconstruct market value from price and shares outstanding.
FMP's Historical Market Cap endpoint returns historical market capitalization records for a requested symbol. The response is simple: symbol, date, and market cap. That makes it a strong free API test case for developers who want to validate an endpoint, inspect the JSON structure, and decide whether historical market cap data belongs in a larger dashboard, screener, or research workflow.
For free-plan users, the value is the sandbox. You can test authentication, request formatting, supported-symbol behavior, response fields, and parsing logic before deciding whether you need broader coverage, deeper history, higher limits, or production access.
Key Takeaways
- The Historical Market Cap endpoint returns historical market capitalization records for a supported symbol.
- The response is simple to parse, with fields such as symbol, date, and marketCap.
- A free API key is useful for testing endpoint behavior, supported-symbol access, response structure, and JSON parsing logic.
- Historical market cap is useful for company-size analysis, valuation context, dashboarding, and screening workflows.
- Market cap history is an analytical input. It should not be treated as a stock-price forecast or investment recommendation.
What Historical Market Capitalization Shows
The Historical Market Cap endpoint returns past market capitalization records for a requested company. Each record identifies the symbol, date, and market capitalization value.
This can help answer basic but useful questions:
- How has the company's market value changed over time?
- Did company size expand or contract during a specific period?
- How does market cap movement compare with price movement, earnings releases, or major corporate events?
- Does a dashboard or screener need market cap history instead of only the latest market cap value?
Historical market cap does not explain the full reason a company's value changed. It should be reviewed alongside price history, financial statements, corporate actions, share count context, and broader market conditions. Its role is to provide a clean company-size time series that can support additional analysis.
Step 1: Create a Free FMP API Key
Before making requests, create an FMP account and copy your API key from the developer dashboard. The key authenticates your request and lets you test supported endpoints from a script, notebook, API client, or application prototype.
You can review current access tiers on the FMP pricing page, manage your key from the developer dashboard, or create an account through the FMP registration page.
For this workflow, the free plan is useful because it gives you a real testing environment. The goal is not to build a full production market data system immediately. The goal is to validate the endpoint:
- Can you authenticate successfully?
- Does the endpoint return the expected fields?
- Can your code parse symbol, date, and marketCap?
- Does the response fit your dataframe, chart, table, or dashboard component?
- Do you need broader coverage, more history, higher limits, or production access before scaling?
That makes the free plan useful for indie developers, students, analysts, and product builders who want to test FMP APIs before building a larger workflow around them.
Step 2: Retrieve Historical Market Cap for a Supported Symbol
With your API key ready, you can issue a direct HTTP GET request to test the endpoint.
Verified Request URL:
https://financialmodelingprep.com/stable/historical-market-capitalization?symbol=AAPL&apikey=YOUR_API_KEY
Replace YOUR_API_KEY with your own key.
A sample response may look like this:
[
{
"symbol": "AAPL",
"date": "2026-06-10",
"marketCap": 4289351154440
},
{
"symbol": "AAPL",
"date": "2026-06-09",
"marketCap": 4274199114900
}
]
For a free-plan test, the important part is not building the largest possible dataset on the first request. Start with one supported symbol, confirm the response structure, parse the fields, and decide whether the endpoint fits the workflow you are building.
Step 3: Understand the Historical Market Cap Fields
The response is intentionally simple.
- symbol: The ticker requested in the API call.
- date: The date associated with the historical market cap record.
- marketCap: The company's market capitalization value for that date.
Because market capitalization values can be very large, your code should treat marketCap as a numeric field that can handle large integers. If you plan to chart the data, you may also want to convert market cap into billions or trillions for readability.
For example, instead of displaying 4289351154440, a dashboard might show approximately $4.29T.
Step 4: What You Can Test With a Free API Key
The free plan is best used as a sandbox. It helps you test endpoint mechanics before deciding whether you need broader access.
For historical market cap data, a free API workflow can help validate:
|
Free Plan Test Area |
What It Lets You Validate |
|
Authentication |
Whether your API key works in the request URL |
|
Supported symbols |
Whether your requested symbol is available for testing |
|
Response shape |
Whether the endpoint returns symbol, date, and marketCap |
|
Field parsing |
Whether your code can parse market cap as a numeric field |
|
Chart logic |
Whether your chart can display large market cap values cleanly |
|
Workflow fit |
Whether historical market cap belongs in your dashboard, screener, or research view |
The free plan should not be treated as a full production data layer. If your project needs broader symbol coverage, deeper history, higher request volume, scheduled refreshes, commercial use, or production reliability, use the free test to validate the endpoint first. Then match the workflow to the plan that supports the scale and access you need.
Step 5: Use Historical Market Cap With Other Financial Data
Historical market cap is most useful when it is used as context, not as a standalone conclusion.
For example, a company's market cap may rise because the stock price increased, because shares outstanding changed, or because both moved at the same time. If market cap changes sharply, a useful next step is to compare it with historical prices, adjusted price history, corporate actions, financial statement trends, or major company events.
Historical market cap can support several practical workflows:
- Company-size trend charts
- Market cap comparison dashboards
- Portfolio or watchlist size tracking
- Valuation context around earnings periods
- Screening logic based on company size
- Research views that compare market cap against revenue, earnings, or cash flow trends
If you are building a valuation or screening workflow, market cap can also sit beside other FMP datasets. For example, adjusted and unadjusted stock price data can help explain how splits and dividends affect historical price series. Historical rating scores can add a separate view of financial score history. Together, these datasets can help you test whether a broader FMP workflow fits your app or research process.
Why Historical Market Cap Is Useful
Historical market cap is useful because it turns company size into a time series. Instead of looking only at today's market value, you can see how the market value changed across days, months, earnings periods, or major company events.
For an indie developer, this is a practical endpoint to test because the response is simple and easy to display. You can build a small chart, table, or watchlist module without starting with a complex financial statement workflow. For an analyst, historical market cap can help frame company-size movement before moving into deeper valuation, fundamentals, or price analysis.
A good first project is simple: request historical market cap for one supported symbol, parse the response, convert marketCap into billions or trillions, and plot the values over time. If that works, you can decide whether to add price history, adjusted prices, financial statements, ratings, or other datasets.
Other Free API Workflows to Test
Once the historical market cap request is working, the same request-and-parse pattern can be reused across other free API workflows. The goal is to test one endpoint at a time, inspect the response, and decide whether the data fits your product or research workflow.
Useful next tests include:
- Compare adjusted and unadjusted stock prices when you want to understand how splits and dividends affect historical price data.
- Retrieve historical rating scores when you want to test financial score fields for supported symbols.
- Analyze IPO filings and prospectuses when your workflow needs filing context for new public companies.
- Track company headcount and workforce changes when you want to test another company-level time-series dataset.
- Retrieve company share float data when you want share structure context alongside market cap or valuation work.
- Retrieve market movers, gainers, losers, and most active stocks when you want to test a market activity endpoint.
- Handle delisted companies and historical symbols when your project needs better symbol lifecycle handling.
Together, these pages create a practical testing path. Start with one endpoint, confirm the response, parse the fields, and then add related datasets only when they help the workflow.
When to Upgrade Beyond the Free Plan
A free API key is useful for testing endpoint behavior and building small prototypes. It is not always enough for a larger workflow.
You may need to review a paid plan when your project requires:
- more symbols
- more frequent requests
- deeper historical coverage
- scheduled refreshes
- production dashboards
- commercial or customer-facing use
- broader endpoint access
- higher reliability expectations
A good rule is to build the smallest useful test first. If the endpoint structure works and the data fits your project, then review the plan options that match the scale of the workflow. FMP also has resources for choosing the right plan and understanding when an account upgrade makes sense for a larger workflow.
FAQs
What does the Historical Market Cap API return?
The endpoint returns historical market capitalization records for a requested symbol. Each record can include fields such as symbol, date, and marketCap.
Is the Historical Market Cap API available on the free plan?
The free plan can be used to test supported endpoint behavior, response structure, and parsing logic. Available symbols, historical depth, and endpoint access can vary by account or plan, so users should confirm current access in their account before building a larger workflow.
What can I test with a free API key?
You can test authentication, request formatting, supported-symbol behavior, response fields, JSON parsing, and whether historical market cap data fits your chart, table, dashboard, or research workflow.
Can I use historical market cap to predict stock performance?
No. Historical market cap shows how a company's market value changed over time. It can support research and dashboarding, but it should not be treated as a stock-price forecasting tool.
Why is historical market cap useful if I already have historical prices?
Historical prices show the price per share. Historical market cap shows total equity market value. Market cap is often more useful when comparing company size, building watchlists, creating screening logic, or putting price movement into broader valuation context.
Does market cap adjust for stock splits?
Market cap reflects the company's market value for a given date. If you are analyzing price movement around stock splits, dividends, or other corporate actions, compare market cap history with adjusted and unadjusted price history so you understand how the price series is being treated.
What is a good first project with this endpoint?
A good first project is a simple market cap history chart for one supported symbol. Pull the endpoint response, parse date and marketCap, convert market cap into billions or trillions, and display the values in a table or line chart.
