OTP SMS Going Over 160 Characters? Fix Guide

SMS has hard character limits. OTP templates that go over the limit silently fragment into multiple SMS, doubling cost and sometimes confusing the user.

SMS Character Limits

• GSM-7 (English / basic Latin): 160 chars per part.
• UCS-2 (Unicode, Hindi, etc.): 70 chars per part.
• Multi-part overhead: 7 chars per segment for the join header.

GSM-7 vs UCS-2

Stick to GSM-7-safe characters (basic Latin) to keep your OTP at 160 chars. A single Unicode character pushes the entire SMS to UCS-2 — meaning 70-char limit per part.

Multi-Part SMS

Carriers reassemble parts on arrival, but DLR is per-part. A partial-delivery condition is possible (rare).

Cost Impact

• 1 part: Rs 0.25.
• 2 parts: Rs 0.50.
• 3 parts: Rs 0.75.

Tightening Templates

• Drop “Thank you for using {brand}”.
• Drop apostrophes and curly quotes.
• Use “mins” not “minutes”.
• Don’t embed support phone in OTP SMS.

FAQ

StartMessaging templates are defaulted to single-part GSM-7 — you stay at Rs 0.25 / OTP without thinking about encoding.