Credits are the number of SMS you currently have in your account. When you send an SMS, your credits get deducted accordingly. Credit Deduction refers to the number of credits deducted from your balance for sending the message.
When you send an SMS in English the credit limit is 150-160 characters whereas in the Unicode option i.e. when you send SMS in other languages, the limit is 55-70 characters.
In case, of transactional messaging, an OPT-OUT SMS is sent to the DND numbers for which an extra credit is deducted.
You will be able to see the credits consumed by your content on the top right corner of the Text box.
The value for a single credit in English is 160 characters. With the number of characters increasing, the second credit consists of 306 characters and moving on in this manner the value of credit deduction increases by adding 153 characters in the SMS every time. As the number of characters keeps on increasing the number of credits deducted will also increase according to that.
For Unicode the credit calculation as below: