Is it true that some pretax offerings from full time employment at a company can only be taken advantage of via payroll deduction? Essentially your company shuffles the money about for you as the unpaid tax collector, of which you can only specify how much to contribute and to what program. But apart from that company you can never direct money into those accounts yourself. To take advantage of the maximal contribution of a given account you must do so during the limited number of pay periods for that tax year and if you miss it you can never make up for it after the fact.
Some of the deductions that are only available as payroll deductions are:
- Health insurance (medical, dental, vision)
- Up to $50,000 of Term Life insurance
- Disability insurance
- Flex Spending Accounts
- Employer sponsored retirement plan contributions (such as 401(k), 403(b), SEP, etc.)
- Tax-Free Commuter Benefits
There are other deductions you can take if you qualify such as HSA or IRA contributions without any employer help.
You don't offer any specifics, so I'm guessing a little about what you're talking about, but here's a few thoughts:
- You can contribute as much to your 401(k) at the end of the year as your plan and the IRS will allow. If your plan will let you change your election at any time, you could (theoretically) contribute $18,000 to your 401(k) on DEC 31 and get all of the tax benefit. Whether your plan allows changed mid-quarter, would match that amount, etc. are plan-specific.
- For medical insurance, HSAs, etc. the policies will also be specific to your company and insurance providers. If you contribute outside of your payroll system (and thus don't get your withholdings reduced), you may be able to take it as a deduction when you file your taxes and reduce your end-of-year tax bill.
Remember that all tax-related transactions are reconciled when you file. All of your activity for the year is totaled up and (for the most part) when during the year things happen is irrelevant. Your gross taxable income is calculated (which will exclude any "pre-tax" activity, deduction applied (which will any include and "post-tax" deductions), tax liability calculated, and withholdings subtracted to get your net tax due. Whether you have "pre-tax" activity and less tax withheld or "after-tax" activity with a deduction and reduce your net tax, the net effect should be the same.