diff --git a/src/fountain_decoder.c b/src/fountain_decoder.c
index f9c8b29..e63e9d3 100644
--- a/src/fountain_decoder.c
+++ b/src/fountain_decoder.c
@@ -1373,6 +1373,61 @@ fountain_decoder_estimated_percent_complete(fountain_decoder_t *decoder) {
   return progress > 0.99 ? 0.99 : progress;
 }
 
+// Weighted-mixed-frames completion estimate. Ports SeedSigner's
+// weight_mixed_frames=True method (helpers/ur2/fountain_decoder.py): count the
+// fully decoded fragments, plus partial credit for fragments that are still
+// only present inside mixed (XOR'd) frames. Each mixed frame contributes
+// 1/(frames mixed) to every index it covers; each index's total contribution
+// is capped at 0.75 so a not-yet-decoded fragment never counts as much as a
+// decoded one (and so the reported percentage cannot decrease mid-decode).
+// Backward-compatible addition — the reference estimate above is unchanged.
+double fountain_decoder_estimated_percent_complete_weighted(
+    fountain_decoder_t *decoder) {
+  if (!decoder)
+    return 0.0;
+  if (fountain_decoder_is_complete(decoder))
+    return 1.0;
+  if (!decoder->expected_part_indexes ||
+      decoder->expected_part_indexes->count == 0)
+    return 0.0;
+
+  size_t parts = decoder->expected_part_indexes->count;
+
+  // Per-index partial scores from the mixed parts. Fragment indexes are in
+  // [0, seq_len) == [0, parts), so a scratch array keyed by index mirrors the
+  // Python dict `mixed_index_scoring`. Fall back to the reference estimate if
+  // the scratch allocation fails.
+  double *scoring = calloc(parts, sizeof(double));
+  if (!scoring)
+    return fountain_decoder_estimated_percent_complete(decoder);
+
+  mixed_parts_hash_t *hash = decoder->mixed_parts_hash;
+  if (hash) {
+    for (size_t b = 0; b < hash->capacity; b++) {
+      for (hash_entry_t *entry = hash->buckets[b]; entry; entry = entry->next) {
+        size_t cnt = entry->key.count;
+        if (cnt == 0)
+          continue;
+        double score = 1.0 / (double)cnt;
+        for (size_t k = 0; k < cnt; k++) {
+          size_t index = entry->key.indexes[k];
+          if (index < parts)
+            scoring[index] += score;
+        }
+      }
+    }
+  }
+
+  double mixed_score = 0.0;
+  for (size_t i = 0; i < parts; i++) {
+    mixed_score += scoring[i] < 0.75 ? scoring[i] : 0.75;
+  }
+  free(scoring);
+
+  double num_complete = (double)decoder->received_part_indexes.count;
+  return (num_complete + mixed_score) / (double)parts;
+}
+
 uint8_t *fountain_decoder_result_message(fountain_decoder_t *decoder) {
   if (!decoder || !decoder->result)
     return NULL;
diff --git a/src/fountain_decoder.h b/src/fountain_decoder.h
index 4b0b876..7ee5030 100644
--- a/src/fountain_decoder.h
+++ b/src/fountain_decoder.h
@@ -77,6 +77,15 @@ size_t fountain_decoder_processed_parts_count(fountain_decoder_t *decoder);
  */
 double fountain_decoder_estimated_percent_complete(fountain_decoder_t *decoder);
 
+/**
+ * Get estimated completion percentage using the weighted-mixed-frames method
+ * (partial credit for fragments still only present inside mixed/XOR'd frames).
+ * @param decoder Pointer to fountain decoder
+ * @return Completion percentage (0.0 to 1.0)
+ */
+double fountain_decoder_estimated_percent_complete_weighted(
+    fountain_decoder_t *decoder);
+
 /**
  * Get result message
  * @param decoder Pointer to fountain decoder
diff --git a/src/ur_decoder.c b/src/ur_decoder.c
index 55178f8..485695b 100644
--- a/src/ur_decoder.c
+++ b/src/ur_decoder.c
@@ -458,6 +458,13 @@ double ur_decoder_estimated_percent_complete(ur_decoder_t *decoder) {
   return fountain_decoder_estimated_percent_complete(decoder->fountain_decoder);
 }
 
+double ur_decoder_estimated_percent_complete_weighted(ur_decoder_t *decoder) {
+  if (!decoder || !decoder->fountain_decoder)
+    return 0.0;
+  return fountain_decoder_estimated_percent_complete_weighted(
+      decoder->fountain_decoder);
+}
+
 ur_decoder_error_t ur_decoder_get_last_error(ur_decoder_t *decoder) {
   return decoder ? decoder->last_error : UR_DECODER_ERROR_NULL_POINTER;
 }
diff --git a/src/ur_decoder.h b/src/ur_decoder.h
index 6d4552c..c4ed058 100644
--- a/src/ur_decoder.h
+++ b/src/ur_decoder.h
@@ -97,6 +97,13 @@ size_t ur_decoder_processed_parts_count(ur_decoder_t *decoder);
  */
 double ur_decoder_estimated_percent_complete(ur_decoder_t *decoder);
 
+/**
+ * Get estimated completion percentage using the weighted-mixed-frames method.
+ * @param decoder Pointer to URDecoder instance
+ * @return Completion percentage (0.0 to 1.0)
+ */
+double ur_decoder_estimated_percent_complete_weighted(ur_decoder_t *decoder);
+
 /**
  * Get last error
  * @param decoder Pointer to URDecoder instance
diff --git a/uUR.c b/uUR.c
index fa02b26..35790cf 100644
--- a/uUR.c
+++ b/uUR.c
@@ -295,18 +295,34 @@ static mp_obj_t ur_decoder_processed_parts_count_py(mp_obj_t self_in) {
 static MP_DEFINE_CONST_FUN_OBJ_1(ur_decoder_processed_parts_count_obj,
                                  ur_decoder_processed_parts_count_py);
 
-// estimated_percent_complete method
-static mp_obj_t ur_decoder_estimated_percent_complete_py(mp_obj_t self_in) {
-  mp_obj_ur_decoder_t *self = MP_OBJ_TO_PTR(self_in);
+// estimated_percent_complete(weight_mixed_frames=False) method.
+// weight_mixed_frames is an opt-in flag: the default (False) returns the
+// original reference estimate byte-for-byte, so existing callers are
+// unaffected; True selects the weighted-mixed-frames method, which gives
+// partial credit for fragments still only present inside mixed/XOR'd frames.
+static mp_obj_t ur_decoder_estimated_percent_complete_py(size_t n_args,
+                                                         const mp_obj_t *pos_args,
+                                                         mp_map_t *kw_args) {
+  static const mp_arg_t allowed_args[] = {
+      {MP_QSTR_weight_mixed_frames, MP_ARG_BOOL, {.u_bool = false}},
+  };
+  mp_arg_val_t parsed[MP_ARRAY_SIZE(allowed_args)];
+  mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args,
+                   MP_ARRAY_SIZE(allowed_args), allowed_args, parsed);
 
+  mp_obj_ur_decoder_t *self = MP_OBJ_TO_PTR(pos_args[0]);
   if (!self->decoder) {
     return mp_obj_new_float(0.0);
   }
 
-  return mp_obj_new_float(ur_decoder_estimated_percent_complete(self->decoder));
+  double pct =
+      parsed[0].u_bool
+          ? ur_decoder_estimated_percent_complete_weighted(self->decoder)
+          : ur_decoder_estimated_percent_complete(self->decoder);
+  return mp_obj_new_float(pct);
 }
-static MP_DEFINE_CONST_FUN_OBJ_1(ur_decoder_estimated_percent_complete_obj,
-                                 ur_decoder_estimated_percent_complete_py);
+static MP_DEFINE_CONST_FUN_OBJ_KW(ur_decoder_estimated_percent_complete_obj, 1,
+                                  ur_decoder_estimated_percent_complete_py);
 
 // URDecoder locals dict
 static const mp_rom_map_elem_t ur_decoder_locals_dict_table[] = {