Quantum computing and Bitcoin: how real is the Q-Day threat?
Could a quantum computer ever crack Bitcoin? We explain what Q-Day is, how vulnerable Bitcoin really is now and what NIST and developers are doing about it — without panic.
It sounds like science fiction, but the question is being asked more and more seriously: could a quantum computer ever crack Bitcoin? In 2026, the topic has stepped out of the techies' corner and gone mainstream. We calmly explain how big the risk really is.
What is ‘Q-Day’?
Q-Day is the hypothetical day on which quantum computers are powerful enough to break the cryptography that secures the internet — and crypto — such as RSA and elliptic-curve cryptography (ECC). Bitcoin uses the latter to protect your holdings. In March 2026, several research papers appeared suggesting that Q-Day may come sooner than thought.
How vulnerable is Bitcoin now?
For now, it's not too bad. On 24 April 2026, independent researcher Giancarlo Lelli cracked a 15-bit ECC key using publicly accessible quantum hardware. Impressive, but Bitcoin uses 256-bit encryption — astronomically much stronger. The network is therefore far from in danger.
Experts do warn that older, ‘exposed’ Bitcoin addresses could become vulnerable over time. This is estimated to involve billions in funds held in addresses whose public key is already visible.
What is being done about it?
Preparation is in full swing:
- NIST, the US standards institute, advises phasing out existing encryption before 2030 and fully replacing it with quantum-resistant methods by 2035 at the latest.
- Within Bitcoin, work is underway on proposals such as BIP-360, with a new type of transaction that uses quantum-resistant signatures.
- 2026 has been declared the ‘Year of Quantum Security’, with support from bodies such as NIST and CISA.
Should you worry?
Most experts expect Q-Day only in the 2030s or later — no one can predict the exact date. So it is not a reason for panic, but it is a reason to follow developments. A practical tip remains: keep long-term holdings safe, for example on a hardware wallet, and do not reuse addresses unnecessarily.
Sources: Decrypt — What Is Q-Day?, crypto.news, NIST Post-Quantum Cryptography roadmap.