If my sister filed a loan due to me on a chapter 13, may I include 3 years of interest on my claim?

Interest at whatever was agreed to in writing. If there is no writing, that may be tricky.

You can claim only the amount which is owed on the date she filed bankruptcy. So all the interest which was earned before the filing would be included but nothing for interest after the filing.

That depends on your loan agreement and the terms of her filed plan. If your loan agreement included interest at a certain rate, then your claim could include interest from the date of the loan to the date of her bankruptcy. From there, her plan would say whether you would get interest. In most cases, unsecured debt does not.

Sure, if the loan provided for the payment of interest, file the claim for the full amount owed to you.

It's the amount owed at the time the Bankruptcy was filed. You do not figure future interest into balance owed at filing. There is a place in the Proof of Claim to list interest rate. Practically speaking, interest rate is not relevant in the majority of claims. Because unless there are facts going toward non-dischargeability (and a complaint filed etc.) and unless the claim is secured, you will be getting 0% interest. To go even further, there may be a partial dividend, or no dividend, to general unsecured claims anyway. This is because unless it's a "100% plan" you would not be getting the full amount owed. There should be a clause in their Plan that states what each type of creditor is to receive. The Trustee may be willing to explain what will be paid out to you under the terms of this plan, so you might give their office a call. Court clerks might be willing to answer very specific questions about Proof of Claim drafting as well and that's the general nature of your question.

You can include interest up to the day that the bankruptcy petition was filed, but not beyond that date. This answer was provided as a public service to a question posed on the Law Q & A website. The answer is based on the information provided and is limited to those facts. Furthermore, the answer is based on California law and their application to bankruptcy law in California. Additional information could change the context of the question and materially change the answer.

You are allowed to claim the interest due to the date of her filing as part of your claim.