diff --git a/moto/ec2/models.py b/moto/ec2/models.py
index efbbeb6fe..dc12f8eba 100644
--- a/moto/ec2/models.py
+++ b/moto/ec2/models.py
@@ -2819,6 +2819,7 @@ class Subnet(TaggedEC2Resource):
         self.vpc_id = vpc_id
         self.cidr_block = cidr_block
         self.cidr = ipaddress.IPv4Network(six.text_type(self.cidr_block), strict=False)
+        self.available_ips = ipaddress.IPv4Network(cidr_block).num_addresses - 5
         self._availability_zone = availability_zone
         self.default_for_az = default_for_az
         self.map_public_ip_on_launch = map_public_ip_on_launch
diff --git a/moto/ec2/responses/subnets.py b/moto/ec2/responses/subnets.py
index c42583f23..e11984e52 100644
--- a/moto/ec2/responses/subnets.py
+++ b/moto/ec2/responses/subnets.py
@@ -53,7 +53,7 @@ CREATE_SUBNET_RESPONSE = """
     <state>pending</state>
     <vpcId>{{ subnet.vpc_id }}</vpcId>
     <cidrBlock>{{ subnet.cidr_block }}</cidrBlock>
-    <availableIpAddressCount>251</availableIpAddressCount>
+    <availableIpAddressCount>{{ subnet.available_ip_addresses }}</availableIpAddressCount>
     <availabilityZone>{{ subnet._availability_zone.name }}</availabilityZone>
     <availabilityZoneId>{{ subnet._availability_zone.zone_id }}</availabilityZoneId>
     <defaultForAz>{{ subnet.default_for_az }}</defaultForAz>
@@ -81,7 +81,7 @@ DESCRIBE_SUBNETS_RESPONSE = """
         <state>available</state>
         <vpcId>{{ subnet.vpc_id }}</vpcId>
         <cidrBlock>{{ subnet.cidr_block }}</cidrBlock>
-        <availableIpAddressCount>251</availableIpAddressCount>
+        <availableIpAddressCount>{{ subnet.available_ip_addresses }}</availableIpAddressCount>
         <availabilityZone>{{ subnet._availability_zone.name }}</availabilityZone>
         <availabilityZoneId>{{ subnet._availability_zone.zone_id }}</availabilityZoneId>
         <defaultForAz>{{ subnet.default_for_az }}</defaultForAz>