I implemented a linear function for a search algorithm, that boosts a document according to its time since upload. So the newer a document the more likely it will be presented for a given search term. Maximum age that will be boosted is 365 days (MaxDays) to a maximum of 10 points (MaxBoost).

float MaxDays = 365
float MaxBoost = 10
float calculatedBoost = MaxBoost - (daysPassedSinceUpload * (MaxBoost / MaxDays))

But I am not yet satisfied with the results. So I wonder if an exponential function would work better, where the y-axis will be hit at 10 and the x-axis at 365 (see image).

Unfortunately it’s been a few years since I last did any exponential function in school. Can you please help me to figure out a working function? All I know for now is that is has to be somthing like y=0.5^x. Obviously different to cross the axis at right spots. Thanks