diff --git a/app/business/leave_calc.py b/app/business/leave_calc.py
new file mode 100644
index 0000000..7624836
--- /dev/null
+++ b/app/business/leave_calc.py
@@ -0,0 +1,36 @@
+from app import db
+from app.models import WorkEntry, LeaveBalance
+import sqlalchemy as sa
+from datetime import date
+
+
+def compute_leave_used(year: int) -> dict[str, int]:
+    start = date(year, 1, 1)
+    end = date(year, 12, 31)
+
+    conges = db.session.scalar(
+        sa.select(sa.func.count()).where(
+            WorkEntry.date.between(start, end),
+            WorkEntry.day_type == "CONGE",
+        )
+    ) or 0
+
+    rtt = db.session.scalar(
+        sa.select(sa.func.count()).where(
+            WorkEntry.date.between(start, end),
+            WorkEntry.day_type == "RTT",
+        )
+    ) or 0
+
+    return {"conges": conges, "rtt": rtt}
+
+
+def get_or_create_balance(year: int) -> LeaveBalance:
+    balance = db.session.scalar(
+        sa.select(LeaveBalance).where(LeaveBalance.year == year)
+    )
+    if balance is None:
+        balance = LeaveBalance(year=year)
+        db.session.add(balance)
+        db.session.commit()
+    return balance
diff --git a/tests/test_leave_calc.py b/tests/test_leave_calc.py
new file mode 100644
index 0000000..f69e4e0
--- /dev/null
+++ b/tests/test_leave_calc.py
@@ -0,0 +1,41 @@
+from app.business.leave_calc import compute_leave_used, get_or_create_balance
+from app.models import WorkEntry, LeaveBalance
+from app import db
+from datetime import date
+import sqlalchemy as sa
+
+
+def test_compute_leave_used_conges(app):
+    with app.app_context():
+        entries = [
+            WorkEntry(date=date(2025, 1, 6), day_type="CONGE"),
+            WorkEntry(date=date(2025, 1, 7), day_type="CONGE"),
+            WorkEntry(date=date(2025, 1, 8), day_type="RTT"),
+            WorkEntry(date=date(2025, 1, 9), day_type="WORK"),
+        ]
+        for e in entries:
+            db.session.add(e)
+        db.session.commit()
+
+        used = compute_leave_used(2025)
+        assert used["conges"] == 2
+        assert used["rtt"] == 1
+
+
+def test_get_or_create_balance_creates_default(app):
+    with app.app_context():
+        balance = get_or_create_balance(2025)
+        assert balance.year == 2025
+        assert balance.conges_total == 28
+        assert balance.rtt_total == 18
+
+
+def test_get_or_create_balance_returns_existing(app):
+    with app.app_context():
+        existing = LeaveBalance(year=2025, conges_total=25, rtt_total=15)
+        db.session.add(existing)
+        db.session.commit()
+
+        balance = get_or_create_balance(2025)
+        assert balance.conges_total == 25
+        assert balance.rtt_total == 15