How to get the number of 'free API calls left' for IBM Watson services?

Question

I'm using IBM Watson machine learning services for a university project. The services are ToneAnalyzer, LanguageTranslator and PersonalityInsights. Each service can be used for free, if I stay under a certain threshold of API calls (for example 2500 for ToneAnalyzer). Is there a way to get the number of used API calls this month or how many API calls are left?

I thought that I might be able to find something like this as a method of the 'IamAuthenticator' object, but couldn't find anything.

    IamAuthenticator authenticator = new IamAuthenticator(Keys.ta_key);
    ToneAnalyzer toneAnalyzer = new ToneAnalyzer("2017-09-21", authenticator);
    toneAnalyzer.setServiceUrl(Keys.ta_url);

Does anybody know whether this is possible and if yes in java? Where is the documentation for this?