Okay, time to get started.
Edit: Updated the calculations.
The number of timelines/endings that exists in Undertale:
- 1 Main Neutral Ending = The main Neutral Route/Ending involves everything that led up to defeating Asgore without killing him but Flowey kills him instead, steals the 6 souls and just before the point that Flowey decides to transport you out of that timeline to his timeline.
- 2 Post-Photoshop Flowey Endings: After defeating Photoshop Flowey in his timeline, you have the option to kill or spare Flowey, which leads to creating 2 alternate Endings:
- If you decide to kill Flowey, he stands there on the grass motionless & faceless, Neutral Ending shows after returning back to the main neutral timeline (I mean, if they were still in the same timeline, then how do different events suddenly happen when you left for like a few mins or something? Nothing important shouldn't have happened in that timeframe if that were the case), Flowey kills Asgore but he decides not to be Photoshop Flowey again after remembering his defeat by you & also mentioning new dialogue every time you re-encounter him to check for any changes in dialogue just before he constantly resets the timeline w/ the 6 souls for each change of dialogue while still remaining dead (Acausality makes that self-explanatory of why that's possible).
- Flowey runs away, suggests you to do a Pacifist ending and in return, he doesn't kill Asgore.
- 2 Pacifist Endings = You either stay or go with Toriel
- 2 Soulless Endings = You stay or go with toriel but the timeline gets altered regardless of what choices you choose at this point
- 3 Genocide Route Endings = 1 Normal and 2 Soulless (choosing either "Do Not" or "Erase" which gives you different dialogues depending on the choice you choose)
- 4 Hard Mode Endings
- 85 Alternate Neutral Endings (4 of the alternate Netural Endings were already mentioned btw and the 4 Hard Mode Endings do not include Fun Values)
- Being Soulless doubles this amount because you were never originally soulless in these Neutral Endings + you get extra dialogue from Flowey when you're soulless too
- 1 Dirty Hacker Ending
- 2 official timelines = According to list of Undertale dialogue directly from the game found in pastebin here, a quiche has its own timeline somehow & So Sorry being in the wrong timeline (both the game and pastebin mentions this).
In total:
- 1 + 3 + 2 + 2 + 3 + (85 × 2) + 1 + 2 + 4 = 188 (Number of Timelines/Endings w/o the 13 reloads of Frisk reseting the timeline or Fun values)
- 26 (Alternate timelines created by Frisk's reloads of reseting the timeline that involves deciding whether to spare or kill Sans due to Sans mentioning that other Sans-es exist)
- 188 + 26 = 214 (Total number of timelines/endings without FUN values)
210 × 100 (Fun Values, changes in each route you do) = 21000 + 4 (Hard Mode doesn't include Fun values, which must be separated from the total) = 21,004
21,004 (Total Timelines/Endings in the PC Version-only)
The PS4 & PS Vita and Nintendo Switch Version are 2 extra parallel timelines where
the PS4 & PS Vita has the exclusive Dog Shrine without Mad Mew Mew in this versio whereas in the Nintendo Switch version,
Mad Mew Mew is in the game instead of Mad Dummy & the Dog Shrine is destroyed, so the total number would be tripled but we have to exclude the Dirty Hacker Ending as its impossible to get that ending in these versions.
The total amount for the Nintendo Switch version is the same as the PS4 & PS Vita, so it gets multiplied by 2 and then added to the total of the PC Version.
In total:
- 209 × 100 = 20900 + 4 = 20900
(20900×2) + 21,004 = 41,800 + 21,004 = 62,804
640 (Total number of timelines/endings without the fun values)
62,804 (Total number of timelines/endings including the fun values for all versions)