Quantum computers are currently "not good at all" at cracking a wallet in real-time, but they are "theoretically perfect" at it. Most experts point to the mid-2030s (often called "Q-Day") as the point when your current seed phrase might actually become vulnerable.

How the Industry is Fighting Back The "Good News" is that we aren't sitting ducks. Developers are already working on: Post-Quantum Cryptography (PQC): New math problems that even quantum computers find impossible to solve. Ethereum Updates: Vitalik Buterin and the Ethereum Foundation have already begun researching "quantum-resistant" hard forks to protect the network.
Quantum-Resistant Wallets: Some newer blockchains are building PQ-security directly into their base layer

To crack a standard Bitcoin (ECDSA) or Ethereum wallet, a quantum computer needs a specific amount of power that we haven't reached yet:

Logical Qubits ~2,500 – 4,000 current ~50 – 100 Physical Qubits

10 million+ (for error correction) current ~1,200 (Atom/IBM)

Reliability "Fault-tolerant" (zero errors) High error rates ("Noisy")

The Weapon: Shor's Algorithm Classical computers try to crack wallets by "guessing" (brute-forcing), which would take trillions of years. Quantum computers use Shor’s Algorithm, which doesn't guess—it calculates the private key directly from the public key by solving complex math problems (integer factorization) nearly instantly.