The latest estimates from the Congressional Budget Office put the cost of building and operating the system at $1.2 trillion over 20 years. That's roughly $1.2 trillion (1,200,000,000,000).
When Trump presented the project a year ago, it was said to cost a comparatively modest $175 billion.
The system is inspired by Israel's "Iron Dome" which protects against rockets, missiles and drones. The US system's protection is primarily intended for long-range threats - ballistic missiles from countries such as North Korea, Iran, China and Russia. It will consist of both ground- and space-based weapons systems.
Trump hopes to have it in use by the end of his term, January 2029.
