diff -r 322f2f20c99a src/script/api/script_town.cpp
--- a/src/script/api/script_town.cpp	Tue Sep 01 22:52:41 2015 +0300
+++ b/src/script/api/script_town.cpp	Wed Oct 14 00:31:27 2015 +0300
@@ -160,23 +160,24 @@
 {
 	EnforcePrecondition(false, IsValidTown(town_id));

+	uint16 growth_rate;
 	switch (days_between_town_growth) {
-		case TOWN_GROWTH_NORMAL:
-			days_between_town_growth = 0;
-			break;
-
-		case TOWN_GROWTH_NONE:
-			days_between_town_growth = TOWN_GROW_RATE_CUSTOM_NONE;
+		case TOWN_GROW_RATE_NORMAL:
+		case TOWN_GROW_RATE_CUSTOM_NONE:
+			growth_rate = days_between_town_growth;
 			break;

 		default:
-			days_between_town_growth = days_between_town_growth * DAY_TICKS / TOWN_GROWTH_TICKS;
-			EnforcePrecondition(false, days_between_town_growth < TOWN_GROW_RATE_CUSTOM);
-			if (days_between_town_growth == 0) days_between_town_growth = 1; // as fast as possible
+			// We are asked for days_between_town_growth * DAY_TICKS,
+			// but town expands every (t->growth_rate + 1) * TOWN_GROWTH_TICKS
+			// Thus selecting growth_rate to make it as close as possible
+			growth_rate = (days_between_town_growth * DAY_TICKS + TOWN_GROWTH_TICKS / 2) / TOWN_GROWTH_TICKS;
+			if (growth_rate > 0) growth_rate--;
+			EnforcePrecondition(false, growth_rate < TOWN_GROW_RATE_UNDEFINED);
 			break;
 	}

-	return ScriptObject::DoCommand(::Town::Get(town_id)->xy, town_id, days_between_town_growth, CMD_TOWN_GROWTH_RATE);
+	return ScriptObject::DoCommand(::Town::Get(town_id)->xy, town_id, growth_rate, CMD_TOWN_GROWTH_RATE);
 }

 /* static */ int32 ScriptTown::GetGrowthRate(TownID town_id)
@@ -187,7 +188,7 @@

 	if (t->growth_rate == TOWN_GROW_RATE_CUSTOM_NONE) return TOWN_GROWTH_NONE;

-	return ((t->growth_rate & ~TOWN_GROW_RATE_CUSTOM) * TOWN_GROWTH_TICKS + DAY_TICKS) / DAY_TICKS;
+	return (((t->growth_rate & ~TOWN_GROW_RATE_CUSTOM) + 1) * TOWN_GROWTH_TICKS + DAY_TICKS / 2) / DAY_TICKS;
 }

 /* static */ int32 ScriptTown::GetDistanceManhattanToTile(TownID town_id, TileIndex tile)
diff -r 322f2f20c99a src/script/api/script_town.hpp
--- a/src/script/api/script_town.hpp	Tue Sep 01 22:52:41 2015 +0300
+++ b/src/script/api/script_town.hpp	Wed Oct 14 00:31:27 2015 +0300
@@ -120,8 +120,8 @@
 	 * Special values for SetGrowthRate.
 	 */
 	enum TownGrowth {
+		TOWN_GROWTH_NORMAL = 0xFFFE,  ///< Use default town growth algorithm instead of custom growth rate.
 		TOWN_GROWTH_NONE   = 0xFFFF,  ///< Town does not grow at all.
-		TOWN_GROWTH_NORMAL = 0x10000, ///< Use default town growth algorithm instead of custom growth rate.
 	};

 	/**
diff -r 322f2f20c99a src/town.h
--- a/src/town.h	Tue Sep 01 22:52:41 2015 +0300
+++ b/src/town.h	Wed Oct 14 00:31:27 2015 +0300
@@ -35,7 +35,9 @@

 static const uint TOWN_GROWTH_WINTER = 0xFFFFFFFE; ///< The town only needs this cargo in the winter (any amount)
 static const uint TOWN_GROWTH_DESERT = 0xFFFFFFFF; ///< The town needs the cargo for growth when on desert (any amount)
+static const uint16 TOWN_GROW_RATE_UNDEFINED   = 0x7FFF; ///< Special value for Town::growth_rate to indicate that it is not calcuted yet
 static const uint16 TOWN_GROW_RATE_CUSTOM      = 0x8000; ///< If this mask is applied to Town::growth_rate, the grow_counter will not be calculated by the system (but assumed to be set by scripts)
+static const uint16 TOWN_GROW_RATE_NORMAL      = 0xFFFE; ///< Special value for CmdTownGrowthRate to switch to normal growth rate calculation
 static const uint16 TOWN_GROW_RATE_CUSTOM_NONE = 0xFFFF; ///< Special value for Town::growth_rate to disable town growth.

 typedef Pool<Town, TownID, 64, 64000> TownPool;
diff -r 322f2f20c99a src/town_cmd.cpp
--- a/src/town_cmd.cpp	Tue Sep 01 22:52:41 2015 +0300
+++ b/src/town_cmd.cpp	Wed Oct 14 00:31:27 2015 +0300
@@ -2596,24 +2596,36 @@
 CommandCost CmdTownGrowthRate(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
 {
 	if (_current_company != OWNER_DEITY) return CMD_ERROR;
-	if ((p2 & TOWN_GROW_RATE_CUSTOM) != 0 && p2 != TOWN_GROW_RATE_CUSTOM_NONE) return CMD_ERROR;
+	if ((p2 & TOWN_GROW_RATE_CUSTOM) != 0 && p2 != TOWN_GROW_RATE_CUSTOM_NONE &&
+	    	p2 != TOWN_GROW_RATE_NORMAL) return CMD_ERROR;
+	if (p2 == TOWN_GROW_RATE_UNDEFINED) return CMD_ERROR;
 	if (GB(p2, 16, 16) != 0) return CMD_ERROR;

 	Town *t = Town::GetIfValid(p1);
 	if (t == NULL) return CMD_ERROR;

 	if (flags & DC_EXEC) {
-		if (p2 == 0) {
-			/* Clear TOWN_GROW_RATE_CUSTOM, UpdateTownGrowRate will determine a proper value */
-			t->growth_rate = 0;
+		if (p2 == TOWN_GROW_RATE_NORMAL) {
+			t->growth_rate = TOWN_GROW_RATE_UNDEFINED;
+		} else if (p2 == TOWN_GROW_RATE_CUSTOM_NONE) {
+			t->growth_rate = p2;
+		} else if (t->growth_rate == TOWN_GROW_RATE_CUSTOM_NONE) {
+			if (t->grow_counter >= p2) {
+				t->grow_counter = p2;
+			}
+			t->growth_rate = p2 | TOWN_GROW_RATE_CUSTOM;
 		} else {
-			uint old_rate = t->growth_rate & ~TOWN_GROW_RATE_CUSTOM;
-			if (t->grow_counter >= old_rate) {
-				/* This also catches old_rate == 0 */
+			if (t->growth_rate != TOWN_GROW_RATE_UNDEFINED) {
+				uint old_rate = t->growth_rate & ~TOWN_GROW_RATE_CUSTOM;
+				if (t->grow_counter >= old_rate) {
+					/* This also catches old_rate == 0 */
+					t->grow_counter = p2;
+				} else {
+					/* Scale grow_counter, so half finished houses stay half finished */
+					t->grow_counter = t->grow_counter * p2 / old_rate;
+				}
+			} else if (t->grow_counter >= p2) {
 				t->grow_counter = p2;
-			} else {
-				/* Scale grow_counter, so half finished houses stay half finished */
-				t->grow_counter = t->grow_counter * p2 / old_rate;
 			}
 			t->growth_rate = p2 | TOWN_GROW_RATE_CUSTOM;
 		}