How to get to level 36 by level 20 (fixing old school levels)

The "Basic D&D" level progression has up to 36 levels. What if I told you you could you could get the same result with 20 levels, and make the game much easier and more intuitive in the process?

(If you don't know Basic D&D, click here).

Even if you're playing B/X or some clone (e.g., OSE, BFRPG, etc.), the game was originally intended to have 36 levels instead of 14, but it was replaced by the BECMI line before that.

In basic games, starting on level 9, your character's HP growth apparently slows down (in fact, it is the opposite: since XP requirements decelerate abruptly, you gain a lot more HP per XP after level 9, comparatively, as explained here).

Contrary to popular belief, this method does not stop HP bloat - it just adds level bloat, as we will illustrate below.

Of course, using 36, 20, or 10 levels is purely arbitrary. However, using 20 levels fits very well with the d20, which is one of the main reasons most modern versions of D&D go to level 20 (with possible expansions). 

Also, counting in fives is intuitive for us five-fingered species, so dividing PCs into tiers: 5, 10, 15, 20, also feels very natural. 5th level PCs are heroes, 10th level PCs are rulers (instead of level 9), 15th level PCs are legendary (beyond the usual B/X 14th levels, so you might avoid these altogether), and by 20th level they are mythic heroes at their peak (these are the Conans, Elrics, etc. of the world).

The table below is the magic-user progression in the RC (I used save versus spells as an example, divide XP by 1000 for simplicity):

As you can see, a level 36 MU has an average of 50 HP (under RC rules, it is likely the MU has no Constitution bonus). 50 HP? You already guessed it - with an average of 1d4 HP per level (2.5), you could get to 50 HP in level 20 if you keep gaining 1d4 per level.

The table below does exactly that - while keeping the XP needed for the same amount of HP unchanged.

So, notice that with 3.300.000 XP the MU still has an average of 43 HP, but it is now level 17 instead of 29. 

Now, let's play with saves a bit. Assume a MU with 3.300.000 XP still has a save of 2 - the best that can be. With 2.850.00 XP he'd have 3. Extrapolate all the way from there, one point per level and... voilá. We don't even need tables anymore. just start at 18 and reduce 1 per level (this is similar to Target 20, of course). 

This does not map perfectly to the RC, but it is close enough for my tastes - and also easier and smoother. 

It also fixes the RC rule (page 32) that states: The maximum damage produced by any single spell—including fire bull, lightening bolt, and delayed blast fireball—is 20 dice, of the type specified (usually d6, therefore a maximum of 20d6). This is very important for game balance, and should not be ignored. For example, without this maximum, a 36th level magic-user could instantly slay any other magic-user by surprise, regardless of the results of the saving throw!

The rule is no longer needed - and now, a 15th level MU casting a 15d6 fireball against a 15th-level fighter is unlikely to kill him in the first try, because the fighter has 15d8 HP!

BTW, you have probably already intuited that you could do the exact same process with the fighter. In the RC, his "THAC0" goes from 19 to 1 over 36 levels. Reduce the fighter to 20 levels, and you have one point of THAC0 improvement per level (similar to AD&D). And thieves' skills could work similarly.

We could use the alternate XP table above, but I prefer simplicity, round numbers and easy formulas over byzantine tables, so just stick with it for the first 10 levels and then go to a flat 400,000 XP per level. This is remarkably close to the original XP requirements per HP. Here is the table for reference:

I'll confess I might require 50,000 XP on level 17 to end with a nice round 5.000.000 on level 20. Also because in my game MUs get 9th level spells on 17, which is another advantage - maximum spell level is always equal to half MU level, round up.

And, for the final twist, I use the same table for all classes. I give a few power-ups (feats), especially for fighters and thieves (who also get 1d6 HP per level - they deserve the boost). Clerics get streamlined a bit, and magic becomes a bit weaker at higher levels, which is good and balanced IMO - even if you're playing B/X and limited to 14 levels.

So, that is what we've got for today... all these ideas are being progressively incorporated in my minimalist OSR game, which you can get for free in the link. All feedback is welcome!

EDIT: I've been told Frank Mentzer mentioned on FB that he wished to have changed it to 20 levels, although I haven't seem it myself. Cool stuff!