Contribution deadlines correspond to the current calendar/tax year.
Deadlines for receiving deposits are adjusted each year towards the end of December. In 2026, deposits must be received in many plans on or prior to December 31st.
Consider paying winter tuition in January instead of December, depending on your 529 balance and tax situation for the prior or next year.
Greg has used most of his funds for his 2 children in college and grad school. He has maxed out his New Mexico tax deductions for the current year. Greg waits until January 3rd, contributes the needed funds for the new year of tax deduction, then pays tuition as soon as possible with the new deposits.
No statement or example on this site should be considered a specific recommendation for your personal situation. Investing and tax strategies each carry significant risks. Examples herein may not apply to your situation. Please consult your estate attorney, tax advisor, or financial advisor for personal advice.