How to use the calculator
Enter the day and time from your HUD. The calculator shows the next horde night, how long until it starts in game time and in real time, and the nights after it.
Set Blood Moon Frequency, Range and Warning, the 24 hour cycle and the daylight length to match your world. If you use a range, add the day of your last horde for an exact window.
Tap "Run the clock" and the in-game time ticks along at your server’s speed, so you can leave the page open next to the game. Copy the link to share it with your group.
How horde nights are timed
The horde starts at dusk, 22:00, on blood moon day. It ends at dawn the next morning. Dusk never moves, but dawn does: it is 22:00 minus the daylight length, so 04:00 by default.
Real time depends on the 24 hour cycle setting, which is how many real minutes one in-game day takes. At 60 minutes, one in-game hour is 2.5 real minutes and a default horde lasts 15 real minutes.
Blood Moon Range explained
With range 0 the horde comes exactly every Frequency days. With a range above 0 it can arrive up to that many days late, picked at random.
The next horde is counted from the day the last one really happened, not from day 0. That is why the calculator asks for your last horde day, and why later windows get wider when it does not know.
Watch the day number: it turns red on horde day at the Blood Moon Warning hour (08:00 by default), so you always get a heads-up.
Changing the settings on your server
V3.x moved blood moon and day length settings into Sandbox Options. Pick the values in the game, copy the code the menu gives you and paste it as the SandboxCode value in serverconfig.xml. The old property lines still sit in some files but V3 ignores them.
On V1.x and V2.x servers, set BloodMoonFrequency, BloodMoonRange, BloodMoonWarning, BloodMoonEnemyCount, DayNightLength and DayLightLength in serverconfig.xml, in the server’s main folder.
Stop the server before you edit the file and start it again after.
Getting ready for horde night
Use the days before the horde to repair your base, craft ammo and set traps. Horde zombies always know where you are and break blocks to reach you, so the walls around your fighting spot matter most.
Be inside before 22:00. With a range above 0, treat every night in the window as horde night until the day number turns red.