Updated October 12, 2026. Quick answer: 10% a year is the line above which a contract is usurious where no statute fixes other rates, and 6% a year is the legal rate when no rate is agreed (Okla. Const. art. XIV and 15 O.S. 266).
Oklahoma promissory note at a glance
| Item | What the documents say |
|---|---|
| Maximum interest rate on a private loan | 10% a year where no legislation fixes other rates; parties may agree to any rate authorized by law |
| Rate if the note names none | 6% a year |
| Penalty for charging too much | Knowingly charging more than the allowed rate forfeits all the interest, and the payer may recover twice the interest paid if suing within two years after maturity |
What Oklahoma law says about interest
Absent any contract as to the rate, the legal rate of interest is six percent (6%) under 15 O.S. 266.
The sources in their own words
- Interest limit: “greater rate of interest than ten percent(10%) per annum” (Oklahoma Constitution Article XIV).
- Exemption or penalty: “shall be deemed a forfeiture of the entire interest” (Oklahoma Constitution Article XIV).
- Rate when none is agreed: “The legal rate of interest shall be six percent (6%)” (Oklahoma Statutes Title 15. Contracts).
- Interest limit: “parties may agree to any rate as may be authorized” (Oklahoma Statutes Title 15. Contracts).
- Time limit to sue: “must be commenced within six (6) years after the due” (Oklahoma Statutes Title 12A. Commercial Code).
- Time limit to sue: “Within five (5) years: An action upon any contract” (Oklahoma Statutes Title 12. Civil Procedure).
If you’re ready to put it in writing
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Signing the note: signature, witness, notary
Under Oklahoma’s UCC 3-401 a person is not liable on an instrument unless the person signed it or an agent signed for them. A note is signed by the person who promises to pay.
None of the sections read for Oklahoma requires a witness or a notary for the note itself. A note secured by real property is a separate question; see what an intra-family mortgage requires.
How long a lender has to sue
Oklahoma gives six years after the due date to sue on a note payable at a definite time (12A O.S. 3-118), and five years on other written contracts (12 O.S. 95).
A worked example: a $20,000 note
Suppose a relative lends you $20,000 and you sign a note for 5 years at 8% a year, paid monthly. With r = 8%/12 and n = 60 months, the level payment is principal times r divided by (1 minus (1 + r) to the power of negative n): $405.53 a month, computed here from these assumed inputs, not quoted. Over the 60 payments that is $24,331.80 in total, of which $4,331.80 is interest.
The 8% rate sits inside the Oklahoma limit in the table above, which is why it was chosen. The federal side of a loan between relatives is covered at family loan minimum interest rate and AFR rates by month.
A loan or a gift?
A loan that may never be repaid is taxed differently; see family loan vs gift, forgiving a family loan and gift tax by state.
What the documents do not say
- No statute read sets a different cap for a private note, so whether the 10% line is the whole rule is a legal question this page does not settle.
- Which of the two time limits governs a particular note is a legal question the documents read do not settle.
- Silence on a witness or notary in the sections read is not proof that no other Oklahoma law requires one.
Common mistakes
- Knowingly charging more than the allowed rate in Oklahoma, which the table gives as 10% where no statute sets other rates, forfeits the entire interest, and the payer may recover twice the interest paid if suing within two years after maturity of the contract (Okla. Const. art. XIV).
- Leaving the rate out: the legal rate of 6% applies when a note names none, and it is rarely what the parties meant.
- Waiting too long to enforce: Oklahoma allows 6 years (note); 5 years (other written contract) to sue on a written note.
Related: promissory notes by state, promissory note requirements, family loan minimum interest rate, and gift tax by state.
Sources
- Oklahoma Constitution Article XIV: https://oksenate.gov/sites/default/files/2022-05/oc14.pdf
- Oklahoma Statutes Title 15. Contracts: https://oklegislature.gov/OK_Statutes/CompleteTitles/os15.pdf
- Oklahoma Statutes Title 12A. Commercial Code: https://oklegislature.gov/OK_Statutes/CompleteTitles/os12a.pdf
- Oklahoma Statutes Title 12. Civil Procedure: https://oklegislature.gov/OK_Statutes/CompleteTitles/os12.pdf
Sources: the primary documents linked above, read on October 12, 2026. General information, not legal or tax advice. Statutes change and courts read them, so confirm anything consequential with a lawyer licensed in your state.