diff --git a/app/Services/Billing/PlanChange.php b/app/Services/Billing/PlanChange.php
index da1c9db..d418953 100644
--- a/app/Services/Billing/PlanChange.php
+++ b/app/Services/Billing/PlanChange.php
@@ -44,10 +44,15 @@ final readonly class PlanChange
         // for it immediately. Prices decide the amount, not the direction.
         $isUpgrade = (int) $target['tier'] > (int) $subscription->tier;
 
-        // Whole days, and never zero: on the last day of a term there is still
-        // a day of service left to charge or refund.
         $termDays = max(1, (int) $subscription->current_period_start->diffInDays($subscription->current_period_end));
-        $remainingDays = (int) max(0, floor($at->diffInDays($subscription->current_period_end, absolute: false)));
+
+        // Rounded UP while any service remains: with less than a day left,
+        // flooring would hand out an upgrade for nothing. Zero only once the
+        // period is genuinely over.
+        $hoursLeft = $at->diffInHours($subscription->current_period_end, absolute: false);
+        $remainingDays = $hoursLeft > 0
+            ? min($termDays, (int) ceil($hoursLeft / 24))
+            : 0;
 
         if (! $isUpgrade) {
             // Downgrade: nothing changes and nothing is owed until the term
@@ -66,6 +71,20 @@ final readonly class PlanChange
             );
         }
 
+        // The period is already over: there is nothing left to prorate, and an
+        // upgrade here belongs to the next term, not to this one.
+        if ($remainingDays === 0) {
+            return new self(
+                isUpgrade: true,
+                allowedNow: false,
+                chargeCents: 0,
+                creditCents: 0,
+                effectiveAt: $subscription->current_period_end->copy(),
+                remainingDays: 0,
+                termDays: $termDays,
+            );
+        }
+
         // Pro rata on both sides: the unused part of what they already paid is
         // worth something, and only the difference is charged.
         $unusedOld = (int) round($subscription->price_cents * $remainingDays / $termDays);
diff --git a/tests/Feature/Billing/PlanChangeTest.php b/tests/Feature/Billing/PlanChangeTest.php
index fc2f799..6ce7f26 100644
--- a/tests/Feature/Billing/PlanChangeTest.php
+++ b/tests/Feature/Billing/PlanChangeTest.php
@@ -178,3 +178,33 @@ it('never invoices a customer for downgrading', function () {
 
     expect($credit)->toBe(0);
 });
+
+it('does not give away an upgrade in the last hours of a term', function () {
+    $start = Illuminate\Support\Carbon::parse('2026-08-01');
+    $subscription = Subscription::factory()->plan('start')->create([
+        'current_period_start' => $start,
+        'current_period_end' => $start->copy()->addMonth(),
+    ]);
+
+    // Six hours left: still service, so still a charge.
+    $change = PlanChange::evaluate($subscription, 'business', Illuminate\Support\Carbon::parse('2026-08-31 18:00'));
+
+    expect($change->remainingDays)->toBe(1)
+        ->and($change->chargeCents)->toBeGreaterThan(0);
+});
+
+it('sends an upgrade requested after the term into the next one', function () {
+    $start = Illuminate\Support\Carbon::parse('2026-08-01');
+    $subscription = Subscription::factory()->plan('start')->create([
+        'current_period_start' => $start,
+        'current_period_end' => $start->copy()->addMonth(),
+    ]);
+
+    // Nothing left to prorate — charging zero and switching immediately would
+    // hand out the bigger plan for free.
+    $change = PlanChange::evaluate($subscription, 'business', Illuminate\Support\Carbon::parse('2026-09-05'));
+
+    expect($change->allowedNow)->toBeFalse()
+        ->and($change->chargeCents)->toBe(0)
+        ->and($change->effectiveAt->toDateString())->toBe('2026-09-01');
+});