diff --git a/esphome/components/logger/logger.cpp b/esphome/components/logger/logger.cpp
index 41aa2313b6..db807f7e53 100644
--- a/esphome/components/logger/logger.cpp
+++ b/esphome/components/logger/logger.cpp
@@ -90,6 +90,25 @@ void HOT Logger::log_vprintf_(uint8_t level, const char *tag, int line, const ch
 #ifdef USE_STORE_LOG_STR_IN_FLASH
 // Implementation for ESP8266 with flash string support.
 // Note: USE_STORE_LOG_STR_IN_FLASH is only defined for ESP8266.
+//
+// This function handles format strings stored in flash memory (PROGMEM) to save RAM.
+// The buffer is used in a special way to avoid allocating extra memory:
+//
+// Memory layout during execution:
+// Step 1: Copy format string from flash to buffer
+//         tx_buffer_: [format_string][null][.....................]
+//         tx_buffer_at_: ------------------^
+//         msg_start: saved here -----------^
+//
+// Step 2: format_log_to_buffer_with_terminator_ reads format string from beginning
+//         and writes formatted output starting at msg_start position
+//         tx_buffer_: [format_string][null][formatted_message][null]
+//         tx_buffer_at_: -------------------------------------^
+//
+// Step 3: Output the formatted message (starting at msg_start)
+//         write_msg_ and callbacks receive: this->tx_buffer_ + msg_start
+//         which points to: [formatted_message][null]
+//
 void Logger::log_vprintf_(uint8_t level, const char *tag, int line, const __FlashStringHelper *format,
                           va_list args) {  // NOLINT
   if (level > this->level_for(tag) || global_recursion_guard_)
@@ -121,7 +140,8 @@ void Logger::log_vprintf_(uint8_t level, const char *tag, int line, const __Flas
   if (this->baud_rate_ > 0) {
     this->write_msg_(this->tx_buffer_ + msg_start);
   }
-  size_t msg_length = this->tx_buffer_at_ - msg_start - 1;  // -1 to exclude null terminator
+  size_t msg_length =
+      this->tx_buffer_at_ - msg_start;  // Don't subtract 1 - tx_buffer_at_ is already at the null terminator position
   this->log_callback_.call(level, tag, this->tx_buffer_ + msg_start, msg_length);
 
   global_recursion_guard_ = false;