So, although we think of April 15 as tax day, taxes are actually due as income is earned, and employers have become the country’s primary tax collectors by withholding taxes from our paychecks. When you retire, you break out of that system: Now it’s up to you to make sure the IRS gets its due when it’s due. If you wait until the following April 15 to send a check, you’re in for a nasty surprise in the form of penalties and interest.

You have two ways to get the job done:

Withholding. Withholding isn’t only for paychecks. If you receive regular payments from a 401(k) plan or company pension, the payers will withhold tax—unless you tell them not to. The same goes for withdrawals from a traditional IRA. That’s right: In retirement, it’s generally up to you whether part of the money will be proactively skimmed off for the IRS.

With 401(k)s, pensions and traditional IRA withdrawals, taxes will be withheld unless you file a Form W-4P to put the kibosh on it. For periodic payments (i.e., payments made in installments at regular intervals over a period of more than one year), withholding is calculated the same way as withholding from wages. When it comes to traditional IRA distributions or other non-periodic payments, withholding will be at a flat 10% rate, unless you request a different rate or block withholding altogether. However, non-IRA distributions that can be rolled over tax-free to an IRA or other eligible retirement plan are generally subject to mandatory 20% withholding—but stay tuned for a way around the 20% withholding.

Things are a little different with Social Security benefits. There will be no withholding unless you specifically ask for it by filing a Form W-4V. You can opt for withholding on Social Security at a 7%, 10%, 12% or 22% rate.

Withholding isn’t necessarily a bad thing, as it stretches your tax bill over the entire year. It might also make life easier if you would otherwise have to make quarterly estimated tax payments.

Quarterly estimated tax payments. The alternative to withholding is to make quarterly estimated tax payments. You need to if you’ll owe more than $1,000 in tax for the year above and beyond what’s covered by withholding. Otherwise, you could face a penalty for underpayment of taxes.