diff --git a/src/lib/schemas/bookings.schema.ts b/src/lib/schemas/bookings.schema.ts
index aa0b298..1016387 100644
--- a/src/lib/schemas/bookings.schema.ts
+++ b/src/lib/schemas/bookings.schema.ts
@@ -1,14 +1,24 @@
 import { z } from 'zod';
 import { idSchema, optionalText, requiredText } from './shared.schema';
 
-export const bookingCreateSchema = z.object({
-	clientId: requiredText('Client'),
-	roomId: requiredText('Room'),
-	serviceId: optionalText(80),
-	startsAt: requiredText('Start time', 40),
-	endsAt: requiredText('End time', 40),
-	status: z.enum(['booked', 'confirmed', 'completed', 'cancelled']).default('booked'),
-	notes: optionalText(1000)
-});
+export const bookingCreateSchema = z
+	.object({
+		clientId: requiredText('Client'),
+		roomId: requiredText('Room'),
+		serviceId: optionalText(80),
+		startsAt: requiredText('Start time', 40),
+		endsAt: requiredText('End time', 40),
+		status: z.enum(['booked', 'confirmed', 'completed', 'cancelled']).default('booked'),
+		notes: optionalText(1000)
+	})
+	.superRefine((data, ctx) => {
+		if (data.startsAt && data.endsAt && data.endsAt <= data.startsAt) {
+			ctx.addIssue({
+				code: 'custom',
+				path: ['endsAt'],
+				message: 'End time must be after the start time.'
+			});
+		}
+	});
 
-export const bookingEditSchema = bookingCreateSchema.extend(idSchema.shape);
+export const bookingEditSchema = bookingCreateSchema.safeExtend(idSchema.shape);
diff --git a/src/lib/server/scheduling.ts b/src/lib/server/scheduling.ts
new file mode 100644
index 0000000..7b38096
--- /dev/null
+++ b/src/lib/server/scheduling.ts
@@ -0,0 +1,140 @@
+import { and, asc, eq, gt, gte, inArray, isNull, lt, lte, ne } from 'drizzle-orm';
+import { db } from '$lib/server/db';
+import { bookings, contracts, contractRooms, rooms } from '$lib/server/db/schema';
+
+const rentableContractRoomTypes = ['private_office', 'coworking_desk'] as const;
+
+export type BookingRoomConflict = {
+	id: string;
+	roomName: string;
+	startsAt: string;
+	endsAt: string;
+};
+
+export type ContractRoomConflict = {
+	contractId: string;
+	roomId: string;
+	roomName: string;
+	startDate: string;
+	endDate: string;
+};
+
+export function bookingIntervalsOverlap(
+	startsAt: string,
+	endsAt: string,
+	existingStartsAt: string,
+	existingEndsAt: string
+) {
+	return startsAt < existingEndsAt && endsAt > existingStartsAt;
+}
+
+export function contractPeriodsOverlap(
+	startDate: string,
+	endDate: string,
+	existingStartDate: string,
+	existingEndDate: string
+) {
+	return startDate <= existingEndDate && endDate >= existingStartDate;
+}
+
+export async function findBookingRoomConflict({
+	organizationId,
+	roomId,
+	startsAt,
+	endsAt,
+	status,
+	excludingBookingId
+}: {
+	organizationId: string;
+	roomId: string;
+	startsAt: string;
+	endsAt: string;
+	status: string;
+	excludingBookingId?: string;
+}): Promise<BookingRoomConflict | null> {
+	if (status === 'cancelled') return null;
+
+	const baseConditions = [
+		eq(bookings.organizationId, organizationId),
+		eq(bookings.roomId, roomId),
+		isNull(bookings.archivedAt),
+		ne(bookings.status, 'cancelled'),
+		lt(bookings.startsAt, endsAt),
+		gt(bookings.endsAt, startsAt)
+	];
+	const where = excludingBookingId
+		? and(...baseConditions, ne(bookings.id, excludingBookingId))
+		: and(...baseConditions);
+
+	const [conflict] = await db
+		.select({
+			id: bookings.id,
+			roomName: rooms.name,
+			startsAt: bookings.startsAt,
+			endsAt: bookings.endsAt
+		})
+		.from(bookings)
+		.innerJoin(rooms, eq(bookings.roomId, rooms.id))
+		.where(where)
+		.orderBy(asc(bookings.startsAt))
+		.limit(1);
+
+	return conflict ?? null;
+}
+
+export async function findActiveContractRoomConflict({
+	organizationId,
+	roomIds,
+	startDate,
+	endDate,
+	excludingContractId
+}: {
+	organizationId: string;
+	roomIds: string[];
+	startDate: string;
+	endDate: string;
+	excludingContractId?: string;
+}): Promise<ContractRoomConflict | null> {
+	const uniqueRoomIds = [...new Set(roomIds)];
+	if (uniqueRoomIds.length === 0) return null;
+
+	const baseConditions = [
+		eq(contracts.organizationId, organizationId),
+		eq(contracts.status, 'active'),
+		isNull(contracts.archivedAt),
+		inArray(contractRooms.roomId, uniqueRoomIds),
+		eq(rooms.organizationId, organizationId),
+		inArray(rooms.type, rentableContractRoomTypes),
+		isNull(rooms.archivedAt),
+		lte(contracts.startDate, endDate),
+		gte(contracts.endDate, startDate)
+	];
+	const where = excludingContractId
+		? and(...baseConditions, ne(contracts.id, excludingContractId))
+		: and(...baseConditions);
+
+	const [conflict] = await db
+		.select({
+			contractId: contracts.id,
+			roomId: contractRooms.roomId,
+			roomName: rooms.name,
+			startDate: contracts.startDate,
+			endDate: contracts.endDate
+		})
+		.from(contractRooms)
+		.innerJoin(contracts, eq(contractRooms.contractId, contracts.id))
+		.innerJoin(rooms, eq(contractRooms.roomId, rooms.id))
+		.where(where)
+		.orderBy(asc(contracts.startDate), asc(rooms.name))
+		.limit(1);
+
+	return conflict ?? null;
+}
+
+export function bookingConflictMessage(conflict: BookingRoomConflict) {
+	return `${conflict.roomName} is already booked from ${conflict.startsAt} to ${conflict.endsAt}.`;
+}
+
+export function contractConflictMessage(conflict: ContractRoomConflict) {
+	return `${conflict.roomName} is already assigned to an active contract from ${conflict.startDate} to ${conflict.endDate}.`;
+}