# FixedInterestOnlyLoan `FixedInterestOnlyLoans` is an ERC-721 contract. Each minted NFT represents a loan that must be paid back to the NFT owner. {% embed url="" %} ### Loan Parameters Each loan is parametrized by: * Underlying token with which funds are lent out and repaid (e.g. USDC) * Principal debt (minting price) * Period payment (interest paid at each installment) * Period length (a period when the borrower pays installments) * Period count (total number of installments) * End date (date of the last installment to be paid together with the principal, set when the loan is started) * Recipient’s address * Grace period (time by which borrower can be late in repayment of each installment) * A canBeRepaidAfterDefault flag that allows a loan to be repaid after a loan was marked as defaulted ### Loan states & state transitions A loan can have one of the possible statuses: `Created`, `Accepted`, `Started`, `Repaid`, `Canceled`, or `Defaulted`. Upon minting the loan status is set to `Created`. In this state, a borrower can accept a loan by calling `acceptLoan(id)` and the loan status is changed to `Accepted`. The NFT owner can call `start(id)` on loans whose status is `Accepted`. When a loan is started the loan end date is calculated for the loan and the loan status is changed to `Started`. The NFT owner can mark loans as canceled whose status is `Created` or `Accepted`. The NFT owner can mark loans as `Defaulted` whose status is `Started` and the current block time is after a current period `endDate + grace`P`eriod` time. The NFT owner can update the loan's `gracePeriod` at any time by calling `updateInstrument(id)`. The NFT owner must call `repay(id, amount)` to recalculate repaid periods and the current period end date. The repaid amount must be equal to the period payment or period payment + principal for the last installment. The loan can be repaid after it was marked as defaulted only if the proper `canBeRepaidAfterDefault` flag was set to true.