diff --git a/backend/database.py b/backend/database.py
index 5ec9af3..e06b964 100644
--- a/backend/database.py
+++ b/backend/database.py
@@ -15,7 +15,11 @@ engine = create_engine(DATABASE_URL, connect_args={"check_same_thread": False})
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 Base = declarative_base()
 
-pwd_context = CryptContext(schemes=["sha256_crypt"], deprecated="auto")
+# bcrypt is the primary scheme (cross-version stable, OpenSSL-native).
+# sha256_crypt is kept as deprecated fallback so legacy hashes still
+# verify; on first successful login the password is re-hashed to bcrypt
+# via verify_and_update().
+pwd_context = CryptContext(schemes=["bcrypt", "sha256_crypt"], deprecated=["sha256_crypt"])
 
 # JWT Settings
 SECRET_KEY = secret.JWT_SECRET if hasattr(secret, 'JWT_SECRET') else "aars-dev-secret-change-in-production"
@@ -34,6 +38,15 @@ def verify_password(plain_password: str, hashed_password: str) -> bool:
     return pwd_context.verify(plain_password, hashed_password)
 
 
+def verify_and_update_password(plain_password: str, hashed_password: str) -> tuple[bool, str | None]:
+    """Verify password and return new hash if rehash is needed.
+
+    Returns (ok, new_hash_or_none). Caller is responsible for committing
+    the new hash to the DB when new_hash is not None.
+    """
+    return pwd_context.verify_and_update(plain_password, hashed_password)
+
+
 def get_password_hash(password: str) -> str:
     return pwd_context.hash(password)
 
diff --git a/backend/main.py b/backend/main.py
index 9503259..93225e2 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -9,7 +9,7 @@ from pathlib import Path
 from typing import Optional, List
 import json
 
-from database import get_db, create_access_token, verify_password, get_password_hash, init_db, Base, engine
+from database import get_db, create_access_token, verify_password, verify_and_update_password, get_password_hash, init_db, Base, engine
 from models import User, AttendanceRecord, Shift, Accident, Holiday, LeaveRecord
 from sqlalchemy import func as sqlfunc
 from schemas import *
@@ -254,9 +254,20 @@ async def startup():
 @app.post("/api/auth/login", response_model=TokenResponse)
 async def login(form_data: LoginRequest, db: Session = Depends(get_db)):
     user = db.query(User).filter(User.email == form_data.email).first()
-    if not user or not verify_password(form_data.password, user.password_hash):
+    if not user:
+        logger.warning("login failed", extra={"context": {"email": form_data.email, "reason": "user_not_found"}})
+        raise HTTPException(status_code=401, detail="Invalid email or password")
+    # verify_and_update returns (ok, new_hash_if_needs_rehash)
+    ok, new_hash = verify_and_update_password(form_data.password, user.password_hash)
+    if not ok:
         logger.warning("login failed", extra={"context": {"email": form_data.email, "reason": "invalid_credentials"}})
         raise HTTPException(status_code=401, detail="Invalid email or password")
+    # Migrate hash scheme in place (e.g. sha256_crypt -> bcrypt) without forcing logout
+    if new_hash:
+        user.password_hash = new_hash
+        db.commit()
+        db.refresh(user)
+        logger.info("password hash upgraded", extra={"context": {"user_id": user.id, "email": form_data.email}})
     set_user_id(user.id)
     access_token = create_access_token({"sub": str(user.id)})
     logger.info("login success", extra={"context": {"user_id": user.id, "email": form_data.email}})
diff --git a/backend/requirements.txt b/backend/requirements.txt
index 3ecddf2..8abd1fb 100644
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@@ -3,7 +3,8 @@ uvicorn[standard]==0.30.6
 sqlalchemy==2.0.35
 pydantic==2.9.2
 python-jose[cryptography]==3.3.0
-passlib==1.7.4
+passlib[bcrypt]==1.7.4
+bcrypt==4.0.1
 python-multipart==0.0.12
 openpyxl==3.1.5
 reportlab==4.2.5