Filtering orders by date bring wrong results
Try something like:

{% set firstDayOfMonth = year ~ "-" ~ month ~ "-01" %}
{% set daysInThisMonth = firstDayOfMonth|date('t') %}
{% set lastDayOfMonth  = year ~ "-" ~ month ~ "-" ~ daysInThisMonth %}

{% set thisMonthsOrders = craft.commerce.orders.dateOrdered('and', '&gt;= ' ~ firstDayOfMonth, '&lt;= ' ~ lastDayOfMonth) %}