It depends entirely on the risk of default of the person you are lending to and whether you can make any recovery from assets if they default.
If there is no risk of default then the risk-free interest rate could be applied. This simply covers the time value of money (i.e. the value of having money rather than not having it). Currently 3 month risk free rates in most countries are very low (around 0.75% in the UK for example, so roughly 0.75%/4 for a three month loan).
But if there is a risk of default then you need to cover that risk with the interest that you are charging. Typically this is done over a whole portfolio of loans so that across the whole book the interest you are charging covers the losses from all defaults (plus the time value of money and any margin you want to make).
If the loan is covered, for example a mortgage loan is backed by the property itself, then the rate can be lower. However there are still costs of default which the interest rate needs to cover.
A rate of 10% over three months is not huge for an individual unsecured loan over three months. For a small loan from a UK high street bank you could be looking at 20% APR (so 5% if you are looking at the rate expressed over three months - it depends how you are expressing the rate).
Best to do lots of research on comparable rates available to make sure you get the best deal.