January 2021 Fed funds futures price in negative rates

Price moves above 100.00
The rate implied by Fed funds futures for periods in the future, is derived by taking 100.00 and subtracting the price of the contract. So if the price is at 99.50 for a contract (just as an example), the rate implied for that month by the market is 100.00 -99.50 or 0.5%.