401(a) defined contribution plan: tax treatment of contributions made outside of payroll

[Reynolds1500]

I have a defined contribution plan (401a) through my work. I was on leave without pay in 2020 and in order to receive the employer matching I made direct payments to the plan through my benefits office. Because the payments were made outside of payroll they were post-tax. Is there a way to claim a tax deduction or to otherwise alleviate the double taxation that will otherwise result from my eventual disbursements in retirement?

Thanks!

[fanfare]

if you paid in off payroll "without pay" how could you be taxed twice ?

[Critter-3]

If you were allowed to make after tax contributions then those will be accounted for by the plan administer as basis and when you take a distribution the contributions will not be taxable. 

[Opus 17 · Accepted solution]

You do not get a tax deduction now, but the plan administrator will keep track of your basis in the account and this will reduce the amount of tax in the future. For example, if 10% of your contributions were made after tax, then 10% of your withdrawals when you retire will be exempt from tax.  You can confirm this by calling the account custodian.

Note to future readers: contributions made outside of payroll deductions are not allowed for 401(k) and 403(b) plans, the 401(a) operates under different rules.