To use the features described, activate process-orders plugin 
 
require 'ib-api' 
ib =  IB::Connection.new
ib.activate_plugin :process_orders, :advanced_account
in your scripts.

IB::Account.preview

The TWS displays the margin-impact of an order via »Order -> Preview«.

IB::Gateway keeps this methodology.

 Account.preview order: {IB::Order} , contract: {IB::Contract}
  ==>  <Order: (...)  @ {price} PreSubmitted #/{order-id} from {client-id}/{account-id}>

Behind the scene, the what_if-Flag on the Limit.order is set. Then the order is placed the usual way. The response from the TWS is recognized through the OpenOrder-Message, which is returned.

Margin Impact

Lets estimate the margin-impact of a limit-order for a S&P 500 Mini-Future.

> ib =  IB::Connection.current
> the_order =  IB::Limit.order size: 1, price: 5800,
> the_contract = IB::Symbols::Futures.es
> preview = ib.clients.first.preview order: the_order, contract: the_contract 
 =>  <Order: LMT GTC buy 1.0  @ 5800.0 PreSubmitted #/1654228057 from {client-id>}/{account-id}
preview.order_state
  =>#<IB::OrderState:0x000075170d1463f8                   
     @attributes=                                                          
      {:status=>"PreSubmitted",                                            
       :init_margin_before=>0.5xxen,                                      
       :maint_margin_before=>0.44xxen,                                  
       :equity_with_loan_before=>0.70xxen,             
       :init_margin_change=>0.22574690000000002e5,        
       :maint_margin_change=>0.13502849999999999e5,       
       :equity_with_loan_change=>-0.20599999999976717e1,  
       :init_margin_after=>0.75xxen,                   
       :maint_margin_after=>0.57xxen,                  
       :equity_with_loan_after=>0.70xxen,

Check Margin

To estimate, if an order will met basic risk-requirements, a handy order.check_margin method is provided.

> ib =  IB::Connection.current
> the_order =  IB::Limit.order size: 100, price: 10
> ford =  IB::Stock.new symbol: 'F'
> ib_clients.first.preview( order: the_order, contract: ford) &.check_margin(0.25) &.place

This example sets up a limit-order to buy Ford-stocks. client.preview provides a new order-object. The check_margin-method analyses the OrderState records and checks it the margin utilization is below the specified treshold. In this case, the order is only placed, if a minimum of 25 % of unused margin is left.

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