diff --git a/.changeset/cost-insights-wise-moons-crash.md b/.changeset/cost-insights-wise-moons-crash.md
new file mode 100644
index 0000000000..1277911059
--- /dev/null
+++ b/.changeset/cost-insights-wise-moons-crash.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-cost-insights': patch
+---
+
+Fixed date calculations incorrectly converting to UTC in some cases. This should be a transparent change.
diff --git a/plugins/cost-insights/src/utils/change.test.ts b/plugins/cost-insights/src/utils/change.test.ts
index 7cc03caa0b..9516dfe270 100644
--- a/plugins/cost-insights/src/utils/change.test.ts
+++ b/plugins/cost-insights/src/utils/change.test.ts
@@ -76,13 +76,13 @@ describe('getPreviousPeriodTotalCost', () => {
       change: changeOf(MockAggregatedDailyCosts),
       trendline: trendlineOf(MockAggregatedDailyCosts),
     };
-    const exclusiveEndDate = '2020-09-30';
+    const inclusiveEndDate = '2020-09-30';
     expect(
       getPreviousPeriodTotalCost(
         mockGroupDailyCost.aggregation,
         Duration.P30D,
-        exclusiveEndDate,
+        inclusiveEndDate,
       ),
-    ).toEqual(100_000);
+    ).toEqual(96_600);
   });
 });
diff --git a/plugins/cost-insights/src/utils/change.ts b/plugins/cost-insights/src/utils/change.ts
index fc50439aad..92057a560e 100644
--- a/plugins/cost-insights/src/utils/change.ts
+++ b/plugins/cost-insights/src/utils/change.ts
@@ -22,7 +22,6 @@ import {
   GrowthType,
   MetricData,
   Duration,
-  DEFAULT_DATE_FORMAT,
   DateAggregation,
 } from '../types';
 import dayjs, { OpUnitType } from 'dayjs';
@@ -73,10 +72,7 @@ export function getPreviousPeriodTotalCost(
   inclusiveEndDate: string,
 ): number {
   const dayjsDuration = dayjs.duration(duration);
-  const startDate = inclusiveStartDateOf(
-    duration,
-    dayjs(inclusiveEndDate).add(1, 'day').format(DEFAULT_DATE_FORMAT),
-  );
+  const startDate = inclusiveStartDateOf(duration, inclusiveEndDate);
   // dayjs doesn't allow adding an ISO 8601 period to dates.
   const [amount, type]: [number, OpUnitType] = dayjsDuration.days()
     ? [dayjsDuration.days(), 'day']
diff --git a/plugins/cost-insights/src/utils/duration.ts b/plugins/cost-insights/src/utils/duration.ts
index 79ea150fc5..27447537cc 100644
--- a/plugins/cost-insights/src/utils/duration.ts
+++ b/plugins/cost-insights/src/utils/duration.ts
@@ -24,23 +24,21 @@ export const DEFAULT_DURATION = Duration.P30D;
  * Derive the start date of a given period, assuming two repeating intervals.
  *
  * @param duration see comment on Duration enum
- * @param exclusiveEndDate from CostInsightsApi.getLastCompleteBillingDate + 1 day
+ * @param inclusiveEndDate from CostInsightsApi.getLastCompleteBillingDate
  */
 export function inclusiveStartDateOf(
   duration: Duration,
-  exclusiveEndDate: string,
+  inclusiveEndDate: string,
 ): string {
   switch (duration) {
     case Duration.P7D:
     case Duration.P30D:
     case Duration.P90D:
-      return moment(exclusiveEndDate)
-        .utc()
+      return moment(inclusiveEndDate)
         .subtract(moment.duration(duration).add(moment.duration(duration)))
         .format(DEFAULT_DATE_FORMAT);
     case Duration.P3M:
-      return moment(exclusiveEndDate)
-        .utc()
+      return moment(inclusiveEndDate)
         .startOf('quarter')
         .subtract(moment.duration(duration).add(moment.duration(duration)))
         .format(DEFAULT_DATE_FORMAT);
@@ -57,13 +55,9 @@ export function exclusiveEndDateOf(
     case Duration.P7D:
     case Duration.P30D:
     case Duration.P90D:
-      return moment(inclusiveEndDate)
-        .utc()
-        .add(1, 'day')
-        .format(DEFAULT_DATE_FORMAT);
+      return moment(inclusiveEndDate).add(1, 'day').format(DEFAULT_DATE_FORMAT);
     case Duration.P3M:
       return moment(quarterEndDate(inclusiveEndDate))
-        .utc()
         .add(1, 'day')
         .format(DEFAULT_DATE_FORMAT);
     default:
@@ -76,7 +70,6 @@ export function inclusiveEndDateOf(
   inclusiveEndDate: string,
 ): string {
   return moment(exclusiveEndDateOf(duration, inclusiveEndDate))
-    .utc()
     .subtract(1, 'day')
     .format(DEFAULT_DATE_FORMAT);
 }
@@ -94,7 +87,7 @@ export function intervalsOf(
 }
 
 export function quarterEndDate(inclusiveEndDate: string): string {
-  const endDate = moment(inclusiveEndDate).utc();
+  const endDate = moment(inclusiveEndDate);
   const endOfQuarter = endDate.endOf('quarter').format(DEFAULT_DATE_FORMAT);
   if (endOfQuarter === inclusiveEndDate) {
     return endDate.format(DEFAULT_DATE_FORMAT);
diff --git a/plugins/cost-insights/src/utils/formatters.ts b/plugins/cost-insights/src/utils/formatters.ts
index 182c567644..8f2b94f997 100644
--- a/plugins/cost-insights/src/utils/formatters.ts
+++ b/plugins/cost-insights/src/utils/formatters.ts
@@ -16,7 +16,7 @@
 
 import moment from 'moment';
 import pluralize from 'pluralize';
-import { Duration, DEFAULT_DATE_FORMAT } from '../types';
+import { Duration } from '../types';
 import { inclusiveEndDateOf, inclusiveStartDateOf } from '../utils/duration';
 
 export type Period = {
@@ -92,11 +92,8 @@ export function formatPercent(n: number): string {
 }
 
 export function formatLastTwoLookaheadQuarters(inclusiveEndDate: string) {
-  const exclusiveEndDate = moment(inclusiveEndDate)
-    .add(1, 'day')
-    .format(DEFAULT_DATE_FORMAT);
   const start = moment(
-    inclusiveStartDateOf(Duration.P3M, exclusiveEndDate),
+    inclusiveStartDateOf(Duration.P3M, inclusiveEndDate),
   ).format('[Q]Q YYYY');
   const end = moment(inclusiveEndDateOf(Duration.P3M, inclusiveEndDate)).format(
     '[Q]Q YYYY',
diff --git a/plugins/cost-insights/src/utils/mockData.ts b/plugins/cost-insights/src/utils/mockData.ts
index 14ff9aecd1..d4ac4cd2df 100644
--- a/plugins/cost-insights/src/utils/mockData.ts
+++ b/plugins/cost-insights/src/utils/mockData.ts
@@ -36,7 +36,7 @@ import {
   getDefaultState as getDefaultLoadingState,
 } from '../utils/loading';
 import { findAlways } from '../utils/assert';
-import { inclusiveStartDateOf } from './duration';
+import { inclusiveEndDateOf, inclusiveStartDateOf } from './duration';
 
 type mockAlertRenderer<T> = (alert: T) => T;
 type mockEntityRenderer<T> = (entity: T) => T;
@@ -228,8 +228,9 @@ export function aggregationFor(
   baseline: number,
 ): DateAggregation[] {
   const { duration, endDate } = parseIntervals(intervals);
+  const inclusiveEndDate = inclusiveEndDateOf(duration, endDate);
   const days = dayjs(endDate).diff(
-    inclusiveStartDateOf(duration, endDate),
+    inclusiveStartDateOf(duration, inclusiveEndDate),
     'day',
   );
 
@@ -244,7 +245,7 @@ export function aggregationFor(
   return [...Array(days).keys()].reduce(
     (values: DateAggregation[], i: number): DateAggregation[] => {
       const last = values.length ? values[values.length - 1].amount : baseline;
-      const date = dayjs(inclusiveStartDateOf(duration, endDate))
+      const date = dayjs(inclusiveStartDateOf(duration, inclusiveEndDate))
         .add(i, 'day')
         .format(DEFAULT_DATE_FORMAT);
       const amount = Math.max(0, last + nextDelta());