Dynamically Caclulated Values with Entity Field Query
I don't think Entity Query supports expression.


In your case, I think you might not even need it as you can workaround.

$value_to_compare = 5 - $user_provided_value;
$query->fieldCondition('field_some_number', 'value', $value_to_compare, '>=');
But if you need to compute value based on columns of database table, you can go ahead with db_select, where you can have addExpression for calculation.

$query->addExpression('table_columns_1 + table_columns_2', 'sum');
$query->having('sum', 5,'>=');