From 2a457c28ae57ee5d37ddc6c7453ae004ed28cf7c Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 25 May 2026 08:43:06 +0000
Subject: [PATCH] feat: add calculateSIP utility with rounded monthly
 projections

Agent-Logs-Url: https://github.com/Tejas164321/FinPal/sessions/c977c4a9-6c5a-491b-83b7-441e7e58963d

Co-authored-by: Tejas164321 <157705337+Tejas164321@users.noreply.github.com>
---
 src/lib/calculators.ts | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 src/lib/calculators.ts

diff --git a/src/lib/calculators.ts b/src/lib/calculators.ts
new file mode 100644
index 0000000..6183e66
--- /dev/null
+++ b/src/lib/calculators.ts
@@ -0,0 +1,36 @@
+export interface SIPProjection {
+  month: number;
+  invested: number;
+  returns: number;
+  gain: number;
+}
+
+export function calculateSIP(
+  monthlyAmount: number,
+  annualReturnRate: number,
+  years: number
+): SIPProjection[] {
+  const totalMonths = Math.max(0, Math.floor(years * 12));
+  const monthlyRate = annualReturnRate / 12 / 100;
+  const projections: SIPProjection[] = [];
+
+  for (let month = 1; month <= totalMonths; month += 1) {
+    const invested = monthlyAmount * month;
+    const returns =
+      monthlyRate === 0
+        ? invested
+        : monthlyAmount *
+          (((Math.pow(1 + monthlyRate, month) - 1) / monthlyRate) *
+            (1 + monthlyRate));
+    const gain = returns - invested;
+
+    projections.push({
+      month: Math.round(month),
+      invested: Math.round(invested),
+      returns: Math.round(returns),
+      gain: Math.round(gain),
+    });
+  }
+
+  return projections;
+}