This difference is also known as the premium/discount. If the Mark Price is above the Index Price, futures on Mushino are trading at a premium. If the opposite is true, futures are trading at a discount.
The purpose of Funding is to eliminate this premium/discount.
The premium is calculated as follows:
((Mark Price - Index Price) / Index Price) * Interest
where Interest is the 8 hour interest rate on the Future's underlying asset.
Once the premium is obtained, the Funding Rate can be calculated by taking the premium and applying a dampener:
Max(dampener, Premium) + Min(dampener, Premium)
The dampener can vary by trading pair. For BTC, it is currently set to 0.01 (1%).
The dampener ensures that the Funding Rate can only ever be within an interval of
To calculate the funding on your position, we must first scale the funding rate to reflect only the interval for which funding takes place:
Scaled Funding Rate = (Funding Interval/Funding Time Window)
where the Funding Time Window is 8 hours and the Funding Interval is 0.5 hours.
Then simply multiply the Scaled Funding Rate with the size of your position to get your funding:
Funding = Scaled Funding Rate * Position Size (BTC)