diff --git a/src/lib/banking/format.ts b/src/lib/banking/format.ts
new file mode 100644
index 0000000..08daa09
--- /dev/null
+++ b/src/lib/banking/format.ts
@@ -0,0 +1,20 @@
+interface CurrencyLike {
+  name?: string | null;
+  codeName?: string | null;
+}
+
+export function currencyLabel(currency?: CurrencyLike | number | null): string {
+  if (typeof currency === "number") return "";
+  if (!currency) return "units";
+  return currency.name || currency.codeName || "units";
+}
+
+export function formatAmount(amount: number, currency?: CurrencyLike | number | null): string {
+  const n = amount.toLocaleString();
+  const label = currencyLabel(currency);
+  return label ? `${n} ${label}` : n;
+}
+
+export function formatDate(date: string | Date): string {
+  return new Date(date).toLocaleString();
+}
diff --git a/src/lib/banking/index.ts b/src/lib/banking/index.ts
new file mode 100644
index 0000000..30173a2
--- /dev/null
+++ b/src/lib/banking/index.ts
@@ -0,0 +1,242 @@
+import type { Payload } from "payload";
+import type { BankAccount, BankTransaction } from "@/payload-types";
+
+export type BankAccountType = "treasury" | "faction" | "personal";
+
+export type BankTransactionType =
+  | "deposit"
+  | "withdrawal"
+  | "transfer"
+  | "payment"
+  | "fee"
+  | "salary"
+  | "adjustment";
+
+export interface ApplyTransactionInput {
+  type: BankTransactionType;
+  fromAccountId?: number;
+  toAccountId?: number;
+  amount: number;
+  fee?: number;
+  memo?: string;
+  actorId?: number;
+}
+
+type PayloadType = Awaited<ReturnType<typeof import("payload").getPayload>>;
+
+async function getAccountOrThrow(payload: PayloadType, id: number): Promise<BankAccount> {
+  const account = (await payload
+    .findByID({ collection: "bank-accounts", id, depth: 0, overrideAccess: true })
+    .catch(() => null)) as unknown as BankAccount | null;
+  if (!account) throw new Error("Account not found.");
+  return account;
+}
+
+export async function getMainCurrencyId(payload: PayloadType): Promise<number | null> {
+  try {
+    const gameRules = await payload.findGlobal({ slug: "game-rules", depth: 0 });
+    const currency = gameRules.mainCurrency;
+    if (typeof currency === "number") return currency;
+    if (currency && typeof currency === "object" && "id" in currency) {
+      return (currency.id as number) ?? null;
+    }
+    return null;
+  } catch {
+    return null;
+  }
+}
+
+export async function getMainCurrencyName(payload: PayloadType): Promise<string | null> {
+  const currencyId = await getMainCurrencyId(payload);
+  if (!currencyId) return null;
+  try {
+    const resource = (await payload.findByID({
+      collection: "resources",
+      id: currencyId,
+      depth: 0,
+      overrideAccess: true,
+    })) as unknown as { name?: string | null; codeName?: string | null } | null;
+    if (!resource) return null;
+    return resource.name || resource.codeName || null;
+  } catch {
+    return null;
+  }
+}
+
+export async function createAccount(
+  payload: PayloadType,
+  input: {
+    name: string;
+    accountType: BankAccountType;
+    ownerFactionId?: number;
+    ownerUserId?: number;
+  },
+): Promise<BankAccount> {
+  const { name, accountType, ownerFactionId, ownerUserId } = input;
+  const currencyId = await getMainCurrencyId(payload);
+  if (!currencyId) {
+    throw new Error("No main currency is set in Game Rules.");
+  }
+  return (await payload.create({
+    collection: "bank-accounts",
+    data: {
+      name,
+      accountType,
+      ownerFaction: ownerFactionId ?? null,
+      ownerUser: ownerUserId ?? null,
+      currency: currencyId,
+      balance: 0,
+      status: "open",
+    },
+    overrideAccess: true,
+    depth: 0,
+  })) as unknown as BankAccount;
+}
+
+export async function ensurePersonalAccount(payload: PayloadType, userId: number): Promise<BankAccount> {
+  const existing = (await payload.find({
+    collection: "bank-accounts",
+    where: {
+      and: [{ accountType: { equals: "personal" } }, { ownerUser: { equals: userId } }],
+    },
+    limit: 1,
+    depth: 0,
+    overrideAccess: true,
+  })) as unknown as { docs: BankAccount[] };
+  if (existing.docs.length > 0) return existing.docs[0];
+
+  const user = (await payload.findByID({
+    collection: "users",
+    id: userId,
+    depth: 0,
+    overrideAccess: true,
+  }).catch(() => null)) as unknown as { username?: string; displayName?: string } | null;
+  const label = user?.displayName || user?.username || `User ${userId}`;
+
+  return createAccount(payload, {
+    name: `${label}'s Account`,
+    accountType: "personal",
+    ownerUserId: userId,
+  });
+}
+
+export async function applyTransaction(
+  payload: PayloadType,
+  input: ApplyTransactionInput,
+): Promise<BankTransaction> {
+  const { type, fromAccountId, toAccountId, amount, fee = 0, memo, actorId } = input;
+
+  if (!fromAccountId && !toAccountId) {
+    throw new Error("A transaction must involve at least one account.");
+  }
+  if (amount <= 0) {
+    throw new Error("Amount must be greater than zero.");
+  }
+  if (type === "transfer" && (!fromAccountId || !toAccountId)) {
+    throw new Error("A transfer requires both a source and a destination account.");
+  }
+
+  const totalDebit = amount + fee;
+
+  const fromAccount = fromAccountId ? await getAccountOrThrow(payload, fromAccountId) : null;
+  const toAccount = toAccountId ? await getAccountOrThrow(payload, toAccountId) : null;
+
+  for (const account of [fromAccount, toAccount]) {
+    if (account && account.status === "closed") {
+      throw new Error(`Account "${account.name}" is closed.`);
+    }
+    if (account && account.status === "frozen") {
+      throw new Error(`Account "${account.name}" is frozen.`);
+    }
+  }
+
+  if (fromAccount && (fromAccount.balance ?? 0) < totalDebit) {
+    throw new Error(
+      `Insufficient funds in "${fromAccount.name}". Available: ${(fromAccount.balance ?? 0).toLocaleString()}, needed: ${totalDebit.toLocaleString()}.`,
+    );
+  }
+
+  const timestamp = new Date().toISOString();
+
+  const transaction = (await payload.create({
+    collection: "bank-transactions",
+    data: {
+      transactionNumber: "",
+      type,
+      fromAccount: fromAccountId ?? null,
+      toAccount: toAccountId ?? null,
+      amount,
+      fee: fee ?? 0,
+      memo: memo ?? null,
+      actor: actorId ?? null,
+      status: "completed",
+      timestamp,
+    },
+    overrideAccess: true,
+    depth: 0,
+  })) as unknown as BankTransaction;
+
+  const fromNewBalance = fromAccount ? (fromAccount.balance ?? 0) - totalDebit : 0;
+  const toNewBalance = toAccount ? (toAccount.balance ?? 0) + amount : 0;
+
+  const entries: {
+    account: number;
+    transaction: number;
+    type: BankTransactionType;
+    amount: number;
+    balanceAfter: number;
+    memo: string;
+    timestamp: string;
+  }[] = [];
+
+  if (fromAccount) {
+    entries.push({
+      account: fromAccount.id,
+      transaction: transaction.id,
+      type,
+      amount: -totalDebit,
+      balanceAfter: fromNewBalance,
+      memo: memo ?? `${type} — out`,
+      timestamp,
+    });
+  }
+  if (toAccount) {
+    entries.push({
+      account: toAccount.id,
+      transaction: transaction.id,
+      type,
+      amount,
+      balanceAfter: toNewBalance,
+      memo: memo ?? `${type} — in`,
+      timestamp,
+    });
+  }
+
+  for (const entry of entries) {
+    await payload.create({
+      collection: "ledger-entries",
+      data: entry,
+      overrideAccess: true,
+      depth: 0,
+    });
+  }
+
+  if (fromAccount) {
+    await payload.update({
+      collection: "bank-accounts",
+      id: fromAccount.id,
+      data: { balance: fromNewBalance },
+      overrideAccess: true,
+    });
+  }
+  if (toAccount) {
+    await payload.update({
+      collection: "bank-accounts",
+      id: toAccount.id,
+      data: { balance: toNewBalance },
+      overrideAccess: true,
+    });
+  }
+
+  return transaction;
+}