Plan Upgrade/Downgrade for SaaS Application

SaaS: Plan Upgrade and Downgrade

Plan change is one of trickiest billing operations. Stripe handles proportional calculations, but business logic (what happens to data on downgrade) is on developer side.

Upgrade: Immediate Update

export async function upgradeSubscription(
  tenantId: string,
  newPriceId: string
): Promise<void> {
  const subscription = await db.subscription.findUniqueOrThrow({
    where: { tenantId }
  });

  // Stripe auto-recalculates
  // Example: 20 days left of 30, upgrade from $29 to $99
  // Charge = (99 - 29) * 20/30 = $46.67 immediately
  const updatedSub = await stripe.subscriptions.update(
    subscription.stripeSubscriptionId!,
    {
      items: [{
        id: (await stripe.subscriptions.retrieve(
          subscription.stripeSubscriptionId!
        )).items.data[0].id,
        price: newPriceId,
      }],
      proration_behavior: 'create_prorations',
      payment_behavior: 'error_if_incomplete',
    }
  );

  const previewInvoice = await stripe.invoices.retrieveUpcoming({
    customer: subscription.stripeCustomerId,
    subscription: subscription.stripeSubscriptionId!,
    subscription_items: [{
      id: updatedSub.items.data[0].id,
      price: newPriceId,
    }],
    subscription_proration_behavior: 'create_prorations',
  });

  console.log('Charge now:', previewInvoice.amount_due / 100);
}

Preview Amount for UI

export async function POST(request: Request) {
  const { newPriceId } = await request.json();
  const tenant = await getCurrentTenant();
  const subscription = await db.subscription.findUnique({
    where: { tenantId: tenant!.id }
  });

  const preview = await stripe.invoices.retrieveUpcoming({
    customer: subscription!.stripeCustomerId,
    subscription: subscription!.stripeSubscriptionId!,
    subscription_items: [{
      id: (await stripe.subscriptions.retrieve(
        subscription!.stripeSubscriptionId!
      )).items.data[0].id,
      price: newPriceId,
    }],
  });

  return Response.json({
    amountDue: preview.amount_due / 100,
    currency: preview.currency,
    periodEnd: new Date(preview.period_end * 1000),
  });
}

Downgrade: At Period End

export async function scheduleDowngrade(
  tenantId: string,
  newPriceId: string
): Promise<void> {
  const subscription = await db.subscription.findUniqueOrThrow({
    where: { tenantId }
  });

  await validateDowngrade(tenantId, newPriceId);

  const stripeSubscription = await stripe.subscriptions.retrieve(
    subscription.stripeSubscriptionId!
  );

  await stripe.subscriptions.update(subscription.stripeSubscriptionId!, {
    items: [{
      id: stripeSubscription.items.data[0].id,
      price: newPriceId,
    }],
    proration_behavior: 'none',
    billing_cycle_anchor: 'unchanged',
  });

  await db.subscription.update({
    where: { tenantId },
    data: {
      pendingPriceId: newPriceId,
      pendingPlanChange: getPlanFromPrice(newPriceId),
    }
  });

  await sendPlanChangeScheduledEmail(tenantId, {
    currentPlan: subscription.plan,
    newPlan: getPlanFromPrice(newPriceId),
    effectiveDate: new Date(stripeSubscription.current_period_end * 1000),
  });
}

Downgrade Validation

export async function validateDowngrade(
  tenantId: string,
  newPriceId: string
): Promise<void> {
  const newPlan = getPlanFromPrice(newPriceId);
  const limits = PLAN_LIMITS[newPlan];

  const [projectCount, memberCount, storageGb] = await Promise.all([
    db.project.count({ where: { tenantId } }),
    db.tenantUser.count({ where: { tenantId } }),
    calculateStorageUsage(tenantId),
  ]);

  const violations: string[] = [];

  if (projectCount > limits.projects) {
    violations.push(
      `You have ${projectCount} projects. Limit for ${newPlan}: ${limits.projects}. ` +
      `Delete ${projectCount - limits.projects} projects.`
    );
  }

  if (memberCount > limits.members) {
    violations.push(
      `You have ${memberCount} members. Limit for ${newPlan}: ${limits.members}.`
    );
  }

  if (storageGb > limits.storageGb) {
    violations.push(
      `Used ${storageGb.toFixed(1)} GB. Limit for ${newPlan}: ${limits.storageGb} GB.`
    );
  }

  if (violations.length > 0) {
    throw new PlanDowngradeError(violations);
  }
}

UI: Plan Change Page

export function PlanChangeModal({
  currentPlan,
  targetPlan,
  previewAmount,
  isUpgrade,
  onConfirm,
}: PlanChangeModalProps) {
  return (
    <Dialog>
      <DialogHeader>
        <DialogTitle>
          {isUpgrade ? 'Upgrade' : 'Change'} plan: {currentPlan} → {targetPlan}
        </DialogTitle>
      </DialogHeader>

      {isUpgrade ? (
        <div>
          <p>${previewAmount} will be charged from your card immediately.</p>
          <p>This is proportional payment for the remaining period.</p>
        </div>
      ) : (
        <div>
          <p>Current plan active until end of billing period.</p>
          <p>After that switch to <strong>{targetPlan}</strong>.</p>
          {targetPlan === 'FREE' && (
            <Alert>Check limits: {targetPlan} plan supports up to 3 projects.</Alert>
          )}
        </div>
      )}

      <DialogFooter>
        <Button variant="outline" onClick={onClose}>Cancel</Button>
        <Button onClick={onConfirm}>
          {isUpgrade ? 'Upgrade and Pay' : 'Confirm Plan Change'}
        </Button>
      </DialogFooter>
    </Dialog>
  );
}

Upgrade/downgrade implementation with Stripe proreration, validation and UI — 2–3 working days.