Mo. Rev. Stat. § 86.359: Retroactive payments to be lump sum with interest, rate.

If a retroactive payment is made to a member, surviving spouse, dependent child, or other beneficiary under sections 86.200 to 86.366 for any reason, a lump sum equal to the sum of the retroactive monthly payments, plus interest, shall be paid. For this purpose, interest shall be credited at the rate of six percent annum , compounded annually.