diff --git a/src/features/report/report.models.ts b/src/features/report/report.models.ts
new file mode 100644
index 0000000..ada38ed
--- /dev/null
+++ b/src/features/report/report.models.ts
@@ -0,0 +1,61 @@
+export interface Payor {
+  name: string;
+}
+
+export interface Payee {
+  name: string;
+}
+
+export interface Account {
+  name: string;
+  number: string;
+}
+
+export interface Tag {
+  name: string;
+  icon: string;
+  description: string;
+}
+
+export interface Transaction {
+    payor: Payor;
+    payee: Payee;
+    amount: number;
+    account: Account;
+    tags: Tag[]
+    occurred_at: Date
+}
+
+export interface _PeriodData {
+  sum: number;
+  count: number;
+  average: number;
+  txns: Transaction[];
+}
+
+export interface PeriodData extends _PeriodData {
+  compare?: _PeriodData;
+}
+
+export interface PeriodGroup {
+  group_key: string[];
+  expenses: PeriodData[];
+  incomes: PeriodData[];
+}
+
+export interface Period {
+  id: string;
+  label: string;
+  start: Date;
+  end: Date;
+  groups: PeriodGroup[];
+}
+
+export interface ReportData {
+  period: "weekly" | "monthly" | "yearly" | "fyly" | "full";
+  rolling?: boolean;
+  report_date?: string;
+  group_by?: ("payee" | "tags")[];
+  ignore_self?: boolean;
+  buckets: Period[];
+}
diff --git a/src/features/report/report.utils.ts b/src/features/report/report.utils.ts
new file mode 100644
index 0000000..387f3fe
--- /dev/null
+++ b/src/features/report/report.utils.ts
@@ -0,0 +1,116 @@
+import { ReportData } from "./report.models";
+
+/* ---------- ID BUILDING ---------- */
+
+function formatDate(d: Date): string {
+  const y = d.getUTCFullYear();
+  const m = String(d.getUTCMonth() + 1).padStart(2, "0");
+  const day = String(d.getUTCDate()).padStart(2, "0");
+  return `${y}-${m}-${day}`;
+}
+
+function buildPeriodId(
+  type: ReportData["period"],
+  start: Date,
+  end: Date
+): string {
+  const s = formatDate(start);
+  const e = formatDate(end);
+
+  switch (type) {
+    case "weekly":
+      return `W:${s}_${e}`;
+    case "monthly":
+      return `M:${s}_${e}`;
+    case "yearly":
+      return `Y:${s}_${e}`;
+    case "fyly":
+      return `FY:${s}_${e}`;
+    case "full":
+      return `FULL:${s}_${e}`;
+    default:
+      return `${s}_${e}`;
+  }
+}
+
+/* ---------- LABEL BUILDING ---------- */
+
+const dayFmt = new Intl.DateTimeFormat("en-GB", {
+  day: "numeric",
+  month: "short",
+  timeZone: "UTC",
+});
+
+const monthDayFmt = new Intl.DateTimeFormat("en-GB", {
+  month: "short",
+  day: "numeric",
+  timeZone: "UTC",
+});
+
+const monthFmt = new Intl.DateTimeFormat("en-GB", {
+  month: "short",
+  timeZone: "UTC",
+});
+
+const yearFmt = new Intl.DateTimeFormat("en-GB", {
+  year: "numeric",
+  timeZone: "UTC",
+});
+
+function sameMonth(a: Date, b: Date) {
+  return (
+    a.getUTCFullYear() === b.getUTCFullYear() &&
+    a.getUTCMonth() === b.getUTCMonth()
+  );
+}
+
+function buildLabel(
+  type: ReportData["period"],
+  start: Date,
+  end: Date
+): string {
+  switch (type) {
+    case "weekly":
+      if (sameMonth(start, end)) {
+        const sDay = start.getUTCDate();
+        const eDay = end.getUTCDate();
+        const m = monthFmt.format(start);
+        return `${sDay} ${m} - ${eDay} ${m}`;
+      }
+      return `${dayFmt.format(start)} - ${dayFmt.format(end)}`;
+
+    case "monthly":
+      if (sameMonth(start, end)) {
+        return `${monthFmt.format(start)} ${yearFmt.format(start)}`;
+      }
+      return `${monthDayFmt.format(start)} - ${monthDayFmt.format(end)}`;
+
+    case "yearly":
+      return yearFmt.format(start);
+
+    case "fyly": {
+      const startY = start.getUTCFullYear();
+      const endY = end.getUTCFullYear();
+      return `FY ${startY}–${String(endY).slice(-2)}`;
+    }
+
+    case "full":
+      return `${monthFmt.format(start)} ${yearFmt.format(start)} - ${monthFmt.format(end)} ${yearFmt.format(end)}`;
+
+    default:
+      return `${monthDayFmt.format(start)} - ${monthDayFmt.format(end)}`;
+  }
+}
+
+/* ---------- MAIN ---------- */
+
+export function prepareReport(reportData: ReportData): ReportData {
+  return {
+    ...reportData,
+    buckets: reportData.buckets.map((p) => ({
+      ...p,
+      id: buildPeriodId(reportData.period, p.start, p.end),
+      label: buildLabel(reportData.period, p.start, p.end),
+    })),
+  };
+}