The I.R.S. tool also has a neat refund slider — it’s fun, to the extent that taxes can be — so if you wanted no refund or a $500 refund, you can bake that into the results generated as well.

2. I owed the government money last year for the first time, and it appears that I do again. What happened?

After the 2017 tax law took effect, tax rates generally decreased. So when the government told employers how to tweak the amount of tax they withheld from workers’ paychecks, it mostly suggested decreases, and sometimes filers didn’t withhold enough. If you found yourself in that situation last year — and you didn’t update your withholdings — it is likely to happen again.

But the new law wasn’t the only possible reason. A big life change like marriage, or a job with a new salary, often requires you to tweak your withholdings — but most people don’t.

3. The rules that require minimum withdrawals from retirement accounts changed. How does this affect me?

Until this year, people were generally required to begin withdrawing money from their tax-advantaged retirement accounts when they turned 70½. Now, those who can afford to leave the money untouched can let it sit in those accounts until they are 72. That change came at the end of last year, when legislation called the Secure Act was attached to a much larger spending bill that became law.

What does this mean in practice? If you turned 70½ in 2019, the old rules still apply. That means you have until April 1 to take a required minimum distribution — otherwise you may face a stiff penalty.

But if you reach age 70½ this year or later, you aren’t required to withdraw money right away — you have until April 1 of the year after you reach 72.

Keep in mind that these rules generally apply to employer-sponsored retirement plans as well as traditional individual retirement accounts (but not Roth I.R.A.s, at least while the account owner is still alive). And if taxpayers are still working, they may not have to take minimum withdrawals from their employer’s plan.