title: Calculating RMSE for Prophet Model in Python
body: <p>I'm new to learning python, and I'm creating a time series model which predicts total sales each month using the Prophet model. I am needing help getting the RMSE of my model! Thanks!</p>
  
  <pre><code>from fbprophet import Prophet
  #Creating Dataframe#
  proph = train.groupby(['date_block_num'])[ 'item_cnt_day'].sum()
  proph.index=pd.date_range(start='2013-01-01', end='2015-10-01', freq='MS')
  proph = proph.to_frame().reset_index()
  proph.columns = ['ds', 'y']
  proph.head()
  #Modelling#
  model=Prophet(yearly_seasonality=True)
  model.fit(proph)
  model.head()
  #Making future predictions
  future_data = model.make_future_dataframe(periods=1, freq='MS')
  forecast = model.predict(future_data)
  forecast[['ds', 'yhat', 'yhat_lower', 'yhat_upper']].tail()
  </code></pre>