One of the biggest mistakes entrepreneurs make is not planning adequately for their retirement. This isn’t all that surprising. If you’re self-employed, it’s a squeeze to set the money aside, even if it is tax-deferred. There’s a fear that you may need those funds to keep things rolling if the business doesn’t grow the way you expect, or clients are lax on paying your invoices.

The good news is that Uncle Sam does offer help in a variety of relatively painless plans to help self-employed small-business owners save for retirement in tax-favorable accounts. Here’s a round-up of the three main options:

SEP-IRA If you’re a one-man/woman band, this account is a good bet. A simplified employee pension, or SEP IRA, is a basic way to set aside pretax savings. You can contribute as much as 25 percent of your net self-employment income, up to a maximum of $50,000.

Best features: Flexibility. There’s no need to fund the account until you file your tax return (i.e. there is no requirement that you fund it each year). So if your net income turns out to be higher than expected, you can make a larger contribution and trim your tax bill. If you have a bad year, you can reduce your contribution.  Furthermore, if you’re building your new business on the side while still working for an employer who’s sponsored 401(k) plan you contribute to; your contributions to a SEP don’t interfere with your current workplace plan.

Considerations: This plan may be costly eventually if you have employees, as opposed to contract workers.  The plan requires that you must make the same percentage contributions for all “covered,” workers, or those who are 21 and older who have been employed by you for at least three of the last five years and are expected to earn $550 in the current year. Generally, you can deduct the contributions you make each year to each employee’s SEP-IRA. If you are self-employed, you can deduct the contributions you make each year to your own SEP-IRA.

Tax Filer Tip:   You have until the due date for your tax returns, including any extensions (meaning as late at October 15th), to both set up and fund the plan. You can open SEP-IRA at practically any financial service company including banks, mutual fund companies or brokerage firms. Firms such a Fidelity, Schwab, T. Rowe Price or Vanguard will set up an account gratis and account fees are low or nil.

Solo 401(k) This is a good choice for business owners and their spouses who are able to set aside a significant portion of their earnings. With a solo 401(k), as an employee, you can stash away as much as $17,000. As the employer, you can contribute another 25% of compensation, up to a ceiling of $50,000 including your employee contribution. If you’re 50 or older, you can toss in another $5,500 extra. Total savings: a whopping $55,500.

Best features: Generous contribution limits. If there’s a set-up or annual fee, it will be low. You might pay a small set-up fee, $100 or less, plus an annual fee of $10 to $250. There are no set-up fees, for example, at Fidelity or Vanguard.

And these contribution amounts are optional, so you can save the top figure in flush years and zilch in leaner times. If you already have an individual retirement account funded by money rolled from a previous employer’s 401(k), you can roll those retirement savings into your new solo 401(k).

It’s also possible to take out a loan against a solo 401(k). That can be useful if you need funds in a pinch. You can borrow half the account’s balance, up to $50,000, and normally can take up to five years to pay it back (provider rules differ).  We don’t recommend borrowing from your plan unless it’s a serious situation. But having the option can make it easier to get over the psychological hurdle of opening a retirement account.

Considerations: No extra employees can participate – only self-employed business owners and a spouse. This is not the best option if you’re still working a day job. If you contribute to an employee 401(k) at your day job, you might already be saving the max. You get only one combined $17,000 employee contribution limit to a 401 (k) plan, no matter how many jobs you’re working.

Tax Filer Tip: The deadline to open a new plan is typically December 31^st (or fiscal year end) and must be funded by your tax return due date, plus extension. This is a traditional “qualified” pension. That means you must file an annual Form 5500 report once you have $250,000 of assets in it.  So you may have some paperwork here. Fidelity and Vanguard, for example, provide the information you need for the form, but do not complete or file it for you.

SIMPLE IRA. A SIMPLE IRA is designed specifically for small businesses and self-employed individuals. If you have a few employees, say, less than 10, who make more than $5,000, but far from six figures, and want to offer a plan for them as a perk, this is probably the one for you. It was designed for firms with no more than 100 employees.

For 2012, you can make an employee contribution of up to $11,500 pretax, or $14,000 if you’re 50 or older. There isn’t any percentage of income restrictions. Your contributions are tax deductible, and your investments grow tax deferred until you are ready to make withdrawals in retirement.

A SIMPLE IRA is a little burdensome if you’re a fledgling firm. You’re generally required to make a contribution to match each employee’s salary reduction contributions on a dollar-for-dollar basis up to 3% of the employee’s salary or a flat 2% of pay – no matter what the employee contributes to the account.

Best features: Easy paper work. It should take about 15 minutes or less to fill out the forms.

Considerations: This one isn’t for moonlighters – you can’t contribute if you’ve already maxed out employee contributions to a 401(k) at your day job. Also, if you need to make a withdrawal from a SIMPLE IRA plan within two years of its inception, the 25% penalty is significantly higher than the 10% fee you’d be charged for early withdrawal from a SEP IRA.

Tax Filer Tip: SIMPLE IRAS must be set up by October 1^st to make contributions for that year, and all employee contributions must be made by December 31^st.

For additional guidance on retirement plans for the self-employed, see IRS Publication 560.