What target hash time should I use?

200–500 ms is the standard recommendation for user-facing login. This makes brute-force attacks ~200–500x slower than a 1 ms hash while keeping UX acceptable. For admin or sensitive accounts, use 500–1000 ms. For high-throughput APIs that cannot afford latency, 100 ms is the minimum safe floor.

How do I benchmark my server speed?

Run the hashing function at a fixed baseline cost (e.g. bcrypt cost 10 or PBKDF2 at 100,000 iterations) and time how many hashes per second your server can produce. Tools like `htpasswd -nbBC 10` or Python's `timeit` module work well. Enter that baseline speed and cost; the calculator derives the target from there.

Which algorithm should I choose?

Argon2id is the current best practice (winner of the Password Hashing Competition, recommended by OWASP 2024). bcrypt is battle-tested and widely supported. PBKDF2 is required for FIPS 140-2/3 compliance. Avoid MD5 and SHA-1 for password storage even with high iteration counts — they are too fast.

Why does bcrypt use a cost factor instead of an iteration count?

bcrypt's cost factor N means the algorithm runs 2^N internal rounds. Cost 10 = 1,024 rounds; cost 12 = 4,096 rounds. Each increment doubles compute time, so small numbers have a large effect. The calculator converts your target time into the nearest integer cost factor.

What does "attacker hashes/day" mean?

It estimates how many password guesses an attacker can try per day using a GPU farm (assumed 100× faster than your server). Fewer guesses per day means your users' passwords are safer against offline dictionary attacks.

Hash Iterations Calculator

Name: Hash Iterations Calculator
Availability: InStock
Author: Nham Vu

Enter your server speed (hashes/second) and target hash time to get recommended iteration counts for bcrypt, PBKDF2, and Argon2.

Algorithm Settings

Algorithm

Server speed at baseline (hashes/sec at cost 10)

Measure on your server. Default 100 h/s ≈ a modern CPU core.

Baseline cost factor (for benchmark above)

Target hash time (ms)

Recommended Setting

Click Calculate to see recommendations

Security Analysis

Run the calculator to see attacker effort estimates.

Cost vs. Time (Reference)

Cost	Est. Time (ms)	Attacker guesses/day	Verdict
Run the calculator to populate this table.

Summary

Enter your server speed (hashes/second) and target hash time to get recommended iteration counts for bcrypt, PBKDF2, and Argon2.

How it works

Select your password hashing algorithm (bcrypt, PBKDF2, or Argon2).
Enter your server benchmark speed (hashes per second at the current cost).
Set your target hash time — 200–500 ms is the recommended range for login.
The calculator outputs the recommended cost factor, iteration count, or memory parameters.
Review the security analysis to understand attack resistance at the recommended setting.
Adjust target time up for admin accounts or down for high-traffic APIs.

Use cases

Tune bcrypt cost for a new application before launch.
Upgrade PBKDF2 iterations as hardware gets faster over time.
Compare Argon2id memory vs time trade-offs for your deployment.
Estimate how long an attacker would need to brute-force a password.
Set per-role iteration counts (admin vs regular user).
Document password hashing compliance for security audits.

Frequently Asked Questions

Last updated: 2026-07-08 · Reviewed by Nham Vu