Nice read:

http://www.myrmikan.com/pub/Myrmikan_Research_2018_01_15.pdf

Based on the above article you should have allocation in gold (20% of assets or more) as long as the percentage that the gold on the Federal Reserve’s balance sheet backs its liabilities is below 20%. Once the backing rises above 20%, you should sell your gold.

Today, the Fed reports it holds 8133 tonnes of gold, worth $349.4 billion at $1330 per ounce, which equals 7.9% of the Fed’s reported $4.4 trillion in liabilities. Now is a good time to own gold. Better than in 1968, in fact. (gold backed the Fed’s liabilities by just 12% back then.)