diff --git a/server/src/lib/migration/migrations/recalc-broken-iidx-notecounts.ts b/server/src/lib/migration/migrations/recalc-broken-iidx-notecounts.ts
new file mode 100644
index 000000000..be6eb8ebf
--- /dev/null
+++ b/server/src/lib/migration/migrations/recalc-broken-iidx-notecounts.ts
@@ -0,0 +1,92 @@
+// Charts that had their notecounts changed as the result of a recent discovered
+
+import db from "external/mongo/db";
+import { GenericGetGradeAndPercent } from "lib/score-import/framework/common/score-utils";
+import UpdateScore from "lib/score-mutation/update-score";
+import { GetGamePTConfig } from "tachi-common";
+import type { ScoreDocument, ChartDocument } from "tachi-common";
+import type { Migration } from "utils/types";
+
+// bug in the seeds.
+const recalcChartIDs = [
+	"38ebf85a6b9079bed6acb418cc3866f3a6b6adb7",
+	"88a5f281abf7ce08fde62769edb50b2ed8a1eeb9",
+	"cd89731d004cdcc5292aa10d11c181d8d0545aa5",
+	"8520f95da6f51548adde23ce84bf800e4a19334b",
+	"fcb31b1536d97bfb213cc574462d68d40f9fb15e",
+	"bd67cde14867804902f526c61df59982cb4ffa3e",
+	"241d190af5648d98a91f3b37585d648020d272ff",
+	"7275b7c88df34b6401fb99da7dece2af785cfc4f",
+	"ce71f9c794c429b71ca37ca0615b7b983b3d16ef",
+	"13d6019c21f8fd53b141000c742d4d2a37616aea",
+	"e00c3264172f717675e9c4c2d4ee82f2540a6772",
+	"76b502d2d39861095dc10f691d214bd9f482a815",
+	"4ad68e155dae973d737d7d8ac57453abcc4ac035",
+	"8e60d1ad926add5e84fb6de5a0924c89c365f80f",
+	"a73460d18cf2c6d13a09a46e83073fbd989d2222",
+	"21a475985581c40b616fdfb8ee60d16f64c9bbfa",
+	"a0687bc6951293e803bc121526948dc49aa1394f",
+	"2a80757be4c72f3674c96ff4bdff75deea120892",
+	"37817b02053862c7887f8e30cda23cd5f2c3be4d",
+	"df5543a6822c307dfdbdf162fecf6da013043fff",
+	"828dc62f7cabaf33db72158fdfc5c9ffb89adb4e",
+	"7e7e6866fc5c587a8029aa1bf0bec56441c8c519",
+	"8a51375d59bbe382f9e951d69a8f814b359b570b",
+	"8ce008ee846349caba96edd4538e7a9c148f8af7",
+	"c8805a4e481bb124b6687c44d3d359bdca4dd50e",
+	"adc8458064d179fef6302c12d691f9ff58d92163",
+	"f654276295ca8c228da91c230cc8ac86b23d16e9",
+	"1a856ae72278eedc5ac19050bc1cb441885ac46d",
+	"d87e7aba6edf70bd4b0087165afaa82fad801db3",
+	"85a4e8cebef9a12dddb407ff581f499a078f6010",
+];
+
+const migration: Migration = {
+	id: "recalc-broken-iidx-notecounts",
+	up: async () => {
+		await Promise.all(recalcChartIDs.map((e) => HandleChangedIIDXNotecount(e)));
+	},
+	down: () => {
+		throw new Error(`Reverting this change is not possible.`);
+	},
+};
+
+async function HandleChangedIIDXNotecount(chartID: string) {
+	const scores = await db.scores.find({ chartID });
+	const chart = await db.charts.iidx.findOne({ chartID });
+
+	if (!chart) {
+		throw new Error(`No such chart with the ID ${chartID} exists.`);
+	}
+
+	return Promise.all(scores.map((e) => RecalcPercentForIIDXScore(e, chart)));
+}
+
+function RecalcPercentForIIDXScore(score: ScoreDocument, chart: ChartDocument) {
+	const { percent, grade } = GenericGetGradeAndPercent("iidx", score.scoreData.score, chart);
+
+	const gptConfig = GetGamePTConfig("iidx", score.playtype);
+
+	const gradeIndex = gptConfig.grades.indexOf(grade);
+
+	// shouldn't happen, but lets check anyway.
+	if (gradeIndex === -1) {
+		throw new Error(
+			`Failed to calculate new grade? ${percent} ${grade} on chartID:${chart.chartID}.`
+		);
+	}
+
+	const newScore: ScoreDocument = {
+		...score,
+		scoreData: {
+			...score.scoreData,
+			percent,
+			grade,
+			gradeIndex,
+		},
+	};
+
+	return UpdateScore(score, newScore);
+}
+
+export default migration;