diff --git a/README.md b/README.md
index c21cf41..d5f852e 100644
--- a/README.md
+++ b/README.md
@@ -118,6 +118,9 @@ The exporter returns the following metrics:
 |--------------------------|-----------------------------|-------------|
 | sakuracloud_bill_amount  | Amount billed for the month | `member_id` |
 
+> [!IMPORTANT]
+> This value is updated only once per day. Please ensure the interval is not set too short to avoid unnecessary processing.
+
 #### Coupon
 
 | Metric                            | Description                                          | Labels                           |
@@ -127,6 +130,9 @@ The exporter returns the following metrics:
 | sakuracloud_coupon_exp_date       | Coupon expiration date in seconds since epoch (1970) | `id`, `member_id`, `contract_id` |
 | sakuracloud_coupon_usable         | 1 if coupon is usable                                | `id`, `member_id`, `contract_id` |
 
+> [!IMPORTANT]
+> This value is updated only once per day. Please ensure the interval is not set too short to avoid unnecessary processing.
+
 #### Database
 
 | Metric                                     | Description                                                           | Labels                                                                                                                                                                     |