On GoldHunts data since January 2015, January is the strongest month for XAUUSD with an average return of +3.72% and 72.7% of months positive. Sample sizes are around eleven observations per month, so monthly seasonality is a weak prior for position sizing, not a trading signal.
GoldHunts measures XAUUSD monthly seasonality since January 2015: January is the strongest month at +3.72% average return with 72.7% of months positive, on roughly eleven observations per calendar month.
Monthly seasonality in gold is a weak prior rather than a trading signal, because no month's average return is large relative to gold's monthly volatility at that sample size.
Intraday seasonality is far stronger and better sampled: across 2,599 hourly bars the 13:00 UTC hour averages $24.09 of range versus $2.80 at 21:00 UTC, and New York captures 52.6% of the average daily range.