# Recency weightage on stock forecast error

Say I want to forecast retail stock for 1 month, on daily basis. The error will be calculated using SMAPE, but I would weight the error using recency, i.e., the nearer the weight from now the higher weight. Is there a good weightage scheme I could I adopt?

Something like an exponentially decaying weighting scheme may make sense: weight next week's forecasts with $$1$$, the week's after with $$0.9$$, then $$0.9^2=0.81$$ and so forth.