Constellation Energy is the largest producer of clean energy in the United States. It runs 14 nuclear power stations, plus natural gas plants, hydroelectric dams, wind farms, and solar facilities. Together these assets had 31,676 megawatts of owned generating capacity at the end of 2025. The company makes money two ways: it generates electricity and sells it, and it acts as a retail energy supplier serving about 2 million customer accounts, including three-quarters of the Fortune 100. Revenue came in at $25.5 billion in 2025. Then in January 2026, Constellation acquired Calpine, the nation's largest generator of electricity from natural gas and geothermal sources, adding roughly 23 gigawatts of capacity and making Constellation the largest private-sector power producer in the world. The diagram below traces where the money goes.

Five years of financial data tell a complicated story. Revenue grew from $19.6 billion in 2021 to $25.5 billion in 2025, which looks healthy on the surface. But the path underneath was rough. Operating cash flow was deeply negative in every year from 2021 through 2024, hitting its worst point in 2023 at negative $5.3 billion. Free cash flow, which is the cash left over after capital spending, was also negative across those four years. That means the company was spending more cash than it was bringing in for most of this period.

Then 2025 changed the picture. Operating cash flow swung from negative $2.5 billion in 2024 to positive $4.2 billion in 2025. Free cash flow turned positive at $1.3 billion, the first positive reading across all five years of available data. That single-year reversal is significant, but one year does not confirm a trend. Net debt, which is total borrowings minus cash on hand, stood at $5.3 billion at the end of 2025. That is lower than the $8.8 billion peak in 2023 but higher than the $4.4 billion recorded in 2024, partly reflecting new borrowing tied to the Calpine deal.

The Microsoft deal is not a one-off event. In June 2025, Constellation signed a separate 20-year power purchase agreement with Meta Platforms for the output of its Clinton Clean Energy Center. Big technology companies running data centers need power that runs around the clock, every day of the year. Nuclear power fits that need in a way that wind and solar alone cannot, because the sun does not always shine and the wind does not always blow. These long-term contracts give Constellation a way to lock in revenue from its nuclear plants for decades at a time.

Constellation's nuclear fleet performed at a capacity factor of 94.7 percent in 2025. The industry average runs about four percentage points lower, according to the company's own filings. That means Constellation's plants produce closer to their maximum possible output than most other nuclear operators. The plants generated 183 terawatt-hours of zero-emissions electricity in 2025, enough to power 16 million homes. Nuclear accounted for 68 percent of all the electricity the company generated from its own plants that year.

Now for the risks. The company depends on contracts called power purchase agreements that expire at different times. When those contracts end, Constellation may not be able to find new buyers willing to pay equally good prices. About 70 percent of its power plants sit inside the territory controlled by PJM, a regional power market that covers much of the eastern United States. Changes to PJM's rules or market design could force some older plants to retire early or become unprofitable. Both of these risks sit at the regulatory level, meaning a government decision or market rule change, not just a business mistake, could shrink revenues.

There is also a fuel supply problem specific to nuclear power. Constellation relies partly on Russian uranium to fuel its reactors. A new U.S. law called the Prohibiting Russian Uranium Imports Act became effective in August 2024 and bans most imports of uranium produced in Russia. Russia then issued its own decree restricting enriched uranium exports to the United States. Constellation says it is working with a diverse set of domestic and international suppliers and has built up inventory, but the company openly acknowledges that this situation could affect the longer-term security and cost of its nuclear fuel supply.

Two more risks come directly from the Calpine acquisition. First, when a company pays more for another business than the raw value of its physical assets, the difference is recorded as goodwill on the balance sheet. The Calpine deal at roughly $22 billion is expected to add a significant amount of goodwill. If energy prices fall or business conditions worsen, that goodwill may have to be written down, creating a large loss on paper even if the underlying plants keep running. Second, the company must set aside money in special trust funds to eventually pay for the safe shutdown and cleanup of its nuclear plants. Those future cleanup costs were estimated at $12.9 billion as of December 31, 2025. If the investments inside those trust funds underperform, Constellation may have to contribute billions of dollars more.