There is no standard answer. Each state sets its own definition and exceptions.
Most SOL statutes use the term "date of cause of action" to describe the begin date.
That is the date upon which the creditor could, if they chose, first bring legal action, which would be the date that you have become delinquent under the terms of your account agreement.
That is essentially the same as the definition of what is referred to as the date of first delinquency (DOFD) in the world of credit reporting.
However, some SOL statutes base the period upon the date of last payment, while others are a hybrid, initailly basing the SOL period on the date of cause of action, but providing for reset if payments or firm offers to pay are made.
You must consult the statute for your state to determine the applicable start date, and also the length of the period.
The period itself can also be variable, depending upon the type of debt and periods of non=residency.
States can exempt certain periods of non-residency from the period, or can "borrow" the shorter SOL period from another state if you estsblished the debt in that state, and then moved to your current state of residency.
If any interpretation of terms is required, then it might be necessary to refer to the relevant case law in that state, so if in doubt, consult an attorney.
