Difficulty only estimates based upon party size instead of both party size and party level.

[LinkGaming101]

I've noticed that while building encounters that it doesn't estimate with both values but with just the party size value, so it gives you only a severe encounter with 5 level 1s and a Terrasque. Now while its probably very obvious that 5 level 1s shouldn't face a Terrasque it does make me question other balancing of encounters I have run, but those shouldn't be too far about each other. Still thought this was an issue to bring up and hopefully theres a good way to estimate with both values!

(this is the first time I submit an issue to a repo so hope it shows the picture.)

[PhoneixS]

If you look at the rules, you can see that the budget for a party of 5 members "severe" is 150 = 120 + 30 (because of the 5th member) and for extreme is 200 = 160 + 40, so that's correct. On the other hand, the budget for creatures only goes to "Party Level +4, 160, Extreme-threat solo boss" but your Tarrasque is level 25 is a lot above that "+4" level, but haven't had an official "what if the creature is 4 levels more than the group level". Hence, the app just put the 160.

However, I also think that it could be better to "invent" the extra steps or at least put an if (lvl>+4) => "LEVEL TOO HIGH FOR THE PARTY".

And about the more steps, if you follow the progression approximately, the numbers could be something like:

lvl	XP
5	180
6	220
7	270
8	320
9	370
10	430
11	490
12	550
13	620
14	700
15	780
16	860
17	940
18	1040
19	1130
20	1230
21	1330
22	1440
23	1550
24	1670
25	1790
26	1910
27	2040
28	2170
29	2310
30	2450

So in the example, it would be Tarrasque lvl 25 - 1 lvl party = 24 => 1670XP so you need approximately a group of 38 characters of level 1 to make it an Extreme encounter.

The formula used for the table is round(10+2.1*(lvl+4.1)^2), which isn't perfect but is just an example.

[maxiride]

I agree that the rules should account for bigger differences, however, I'd prefer to not introduce any opinionated ruling as this could introduce more side effects for players using the tool which would see a behaviour undocumented in the rulebook.

put an if (lvl>+4) => "LEVEL TOO HIGH FOR THE PARTY".

That's a nice idea, a warning that clearly informs that the delta of a creature is too high for the party and the xp cost being capped at maximum