About a year and a half ago there was a thread on EN World about Analysis of "Typical" Magic Item Distribution, looking at the treasure generation tables in the DMG.
The rough result is as follows (numbers are per-character):
\begin{array}{ll} \rlap{\textbf{Consumable Items}} \\ \textbf{Level} & \textbf{Every Level} \\ \hline \text{1-5} & \text{1 common} \\ \text{6-10} & \text{1 uncommon} \\ \text{11-15} & \text{1 rare} \\ \text{16-19} & \text{1 very rare} \\ \text{20} & \text{1 legendary} \\ \end{array}
Consumable Items
\begin{array}{ll} \rlap{\textbf{Permanent Items}} \\ \textbf{Level} & \textbf{During this range} \\ \hline \text{1-4} & \text{1st uncommon} \\ \text{5-7} & \text{2nd uncommon} \\ \text{8-10} & \text{1st rare} \\ \text{11-13} & \text{2nd rare} \\ \text{14-16} & \text{1st very rare} \\ \text{17-19} & \text{1st legendary} \\ \end{array}
Level | Every Level |
---|---|
1-5 | 1 common |
6-10 | 1 uncommon |
11-15 | 1 rare |
16-19 | 1 very rare |
20 | 1 legendary |
Permanent Items
Level | During this range |
---|---|
1-4 | 1st uncommon |
5-7 | 2nd uncommon |
8-10 | 1st rare |
11-13 | 2nd rare |
14-16 | 1st very rare |
17-19 | 1st legendary |