diff --git a/src/lib/server/db/schema.ts b/src/lib/server/db/schema.ts
index 7d03f83..548f4f3 100644
--- a/src/lib/server/db/schema.ts
+++ b/src/lib/server/db/schema.ts
@@ -944,6 +944,61 @@ export const companyAccountTransactions = pgTable(
 	]
 );
 
+// ── Recurring Bills ────────────────────────────────────
+
+export const recurringBillCycleEnum = pgEnum('recurring_bill_cycle', [
+	'weekly',
+	'monthly',
+	'quarterly',
+	'yearly'
+]);
+
+export const recurringBillStatusEnum = pgEnum('recurring_bill_status', [
+	'active',
+	'paused',
+	'ended'
+]);
+
+export const recurringBills = pgTable(
+	'recurring_bills',
+	{
+		id: uuid('id').primaryKey().defaultRandom(),
+		companyId: uuid('company_id')
+			.notNull()
+			.references(() => companies.id, { onDelete: 'cascade' }),
+		projectId: uuid('project_id')
+			.notNull()
+			.references(() => projects.id, { onDelete: 'restrict' }),
+		accountId: uuid('account_id')
+			.notNull()
+			.references(() => companyAccounts.id, { onDelete: 'restrict' }),
+		categoryId: uuid('category_id').references(() => categories.id, { onDelete: 'set null' }),
+		partyId: uuid('party_id').references(() => parties.id, { onDelete: 'set null' }),
+		name: text('name').notNull(),
+		description: text('description'),
+		cycle: recurringBillCycleEnum('cycle').notNull(),
+		defaultAmount: numeric('default_amount', { precision: 15, scale: 2 }).notNull(),
+		nextCycleAmount: numeric('next_cycle_amount', { precision: 15, scale: 2 }),
+		currency: text('currency').notNull().default('THB'),
+		dayOfCycle: integer('day_of_cycle'),
+		startDate: date('start_date').notNull(),
+		endDate: date('end_date'),
+		nextDueDate: date('next_due_date').notNull(),
+		lastPostedDate: date('last_posted_date'),
+		status: recurringBillStatusEnum('status').notNull().default('active'),
+		pausedAt: timestamp('paused_at', { withTimezone: true }),
+		skipNext: boolean('skip_next').notNull().default(false),
+		createdBy: text('created_by').references(() => users.id, { onDelete: 'set null' }),
+		deletedAt: timestamp('deleted_at', { withTimezone: true }),
+		createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
+		updatedAt: timestamp('updated_at', { withTimezone: true }).notNull().defaultNow()
+	},
+	(table) => [
+		index('recurring_bills_company_next_due_idx').on(table.companyId, table.nextDueDate),
+		index('recurring_bills_company_status_idx').on(table.companyId, table.status)
+	]
+);
+
 export const companyAddresses = pgTable(
 	'company_addresses',
 	{
@@ -1037,7 +1092,14 @@ export const companyLogEventEnum = pgEnum('company_log_event', [
 	'account_deleted',
 	'account_transaction_added',
 	'account_transfer_posted',
-	'account_reconciled'
+	'account_reconciled',
+	'recurring_bill_created',
+	'recurring_bill_updated',
+	'recurring_bill_deleted',
+	'recurring_bill_paused',
+	'recurring_bill_resumed',
+	'recurring_bill_skipped',
+	'recurring_bill_posted'
 ]);
 
 export const companyLog = pgTable(
diff --git a/src/lib/server/recurring-bills/cycle.ts b/src/lib/server/recurring-bills/cycle.ts
new file mode 100644
index 0000000..e9451dd
--- /dev/null
+++ b/src/lib/server/recurring-bills/cycle.ts
@@ -0,0 +1,94 @@
+export type Cycle = 'weekly' | 'monthly' | 'quarterly' | 'yearly';
+
+function daysInMonthUTC(year: number, monthZeroBased: number): number {
+	return new Date(Date.UTC(year, monthZeroBased + 1, 0)).getUTCDate();
+}
+
+function toUtcMidnight(date: Date): Date {
+	return new Date(Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate()));
+}
+
+function clampDay(year: number, monthZeroBased: number, day: number): number {
+	const max = daysInMonthUTC(year, monthZeroBased);
+	return Math.min(Math.max(day, 1), max);
+}
+
+// Monthly day=31: Jan 31 → Feb 28 → Mar 31 (we never advance based on the previous result alone)
+// Yearly Feb 29 (leap) → Feb 28 next year → Feb 29 in next leap year
+// Quarterly day=31 starting Jan 31 → Apr 30, Jul 31, Oct 31
+// This clamps to month length without losing the "original" day intent across cycles.
+function stepForward(date: Date, cycle: Cycle, targetDay: number | null): Date {
+	const y = date.getUTCFullYear();
+	const m = date.getUTCMonth();
+	const d = date.getUTCDate();
+
+	if (cycle === 'weekly') {
+		return new Date(Date.UTC(y, m, d + 7));
+	}
+
+	const monthDelta = cycle === 'monthly' ? 1 : cycle === 'quarterly' ? 3 : 12;
+	const nextMonth = m + monthDelta;
+	const nextYear = y + Math.floor(nextMonth / 12);
+	const normalisedMonth = ((nextMonth % 12) + 12) % 12;
+	const intendedDay = targetDay ?? d;
+	const clampedDay = clampDay(nextYear, normalisedMonth, intendedDay);
+	return new Date(Date.UTC(nextYear, normalisedMonth, clampedDay));
+}
+
+export function addCycle(date: Date, cycle: Cycle, targetDay: number | null = null): Date {
+	return stepForward(toUtcMidnight(date), cycle, targetDay);
+}
+
+function alignWeekly(startDate: Date, dayOfCycle: number | null): Date {
+	if (dayOfCycle === null) return toUtcMidnight(startDate);
+	const base = toUtcMidnight(startDate);
+	const baseDay = base.getUTCDay();
+	const target = Math.max(0, Math.min(6, dayOfCycle));
+	const delta = (target - baseDay + 7) % 7;
+	return new Date(Date.UTC(base.getUTCFullYear(), base.getUTCMonth(), base.getUTCDate() + delta));
+}
+
+function alignMonthLike(startDate: Date, dayOfCycle: number | null): Date {
+	const base = toUtcMidnight(startDate);
+	if (dayOfCycle === null) return base;
+	const y = base.getUTCFullYear();
+	const m = base.getUTCMonth();
+	const clamped = clampDay(y, m, dayOfCycle);
+	const aligned = new Date(Date.UTC(y, m, clamped));
+	if (aligned.getTime() < base.getTime()) {
+		const nextMonth = m + 1;
+		const nextYear = y + Math.floor(nextMonth / 12);
+		const normalisedMonth = ((nextMonth % 12) + 12) % 12;
+		return new Date(Date.UTC(nextYear, normalisedMonth, clampDay(nextYear, normalisedMonth, dayOfCycle)));
+	}
+	return aligned;
+}
+
+export function computeNextDueDate(
+	startDate: string,
+	cycle: Cycle,
+	dayOfCycle: number | null,
+	from?: Date
+): Date {
+	const start = new Date(`${startDate}T00:00:00Z`);
+	if (Number.isNaN(start.getTime())) {
+		throw new Error(`Invalid startDate: ${startDate}`);
+	}
+	const fromUtc = from ? toUtcMidnight(from) : toUtcMidnight(new Date());
+
+	let candidate =
+		cycle === 'weekly' ? alignWeekly(start, dayOfCycle) : alignMonthLike(start, dayOfCycle);
+
+	while (candidate.getTime() < fromUtc.getTime()) {
+		candidate = stepForward(candidate, cycle, dayOfCycle);
+	}
+
+	return candidate;
+}
+
+export function toIsoDate(date: Date): string {
+	const y = date.getUTCFullYear();
+	const m = String(date.getUTCMonth() + 1).padStart(2, '0');
+	const d = String(date.getUTCDate()).padStart(2, '0');
+	return `${y}-${m}-${d}`;
+}