With the approach of April 15, the dealine for filing federal income taxes, it’s worth remembering the tax gap.

The federal tax gap, or the difference between the amount of income tax owed and the amount collected, is estimated to be $385 billion, more than one-third of recent annual budget deficits.

Some people might wonder why they should care about the tax gap. The answer is simple: For every dollar of taxes not collected by the Internal Revenue Service, the government has to borrow more or increase taxes paid by honest taxpayers.

The tax gap has many causes. Some people make honest mistakes on their tax forms, often due to the overly complex U.S. tax code. Some people simply cheat, by failing to declare income. Some people, often the self-employed or those operating small businesses, sometimes cheat, but in a way they might think is harmless — by overstating their expenses to shield more of their income from taxation. Other people operate in the underground economy, with cash income not reported on their tax forms. It’s all cheating and it all adds to the tax gap.

Then there are the high-profile tax cheats. This group includes people who move money to offshore accounts, beyond the reach of U.S. laws and reporting requirements. When most people think of offshore tax havens they might remember the Cayman Islands, but there are tax havens around the world.

The Tax Justice Network estimates that in 2012 between $21 trillion and $32 trillion was being sheltered from income taxes worldwide through international tax havens.

Tax havens have been in the news recently with the financial crisis in Cyprus, which is recognized as a tax haven for wealthy Russians wanting to hide their money from taxation back home. Similar tax-avoiding climates and secretive banking practices exist in Luxembourg, Switzerland and other countries.

To its credit, the Obama administration has in recent years been forceful in negotiations with Swiss officials to reveal secret accounts held by U.S. citizens. And some progress has been made to expose those holding Swiss bank accounts to track down tax cheats.

Soon after the Cyrpus crisis erupted, Luxembourg came forward to say it will soon allow some daylight to shine on its secretive banking industry. That’s encouraging news and it could encourage other countries to follow suit.

To be effective, any crackdown on tax havens has to be a coordinated international effort.

Earlier this month, a massive document leak was reported, similar to the WikiLeaks release of U.S. foreign affairs documents. In this case, the leak involves thousands of individuals and companies with offshore banking accounts.

The offshore banking leak is said to be more than 100 times larger than the WikiLeaks dump of diplomatic cables. Early reporting reveals that some of the bank accounts belong to very wealthy people, like Wall Street executives and hedge fund managers. But some offshore accounts are also held by the merely rich, like doctors and dentists. As details are revealed, this could help close the tax gap — not only in the U.S. but also in other countries as well.

Closing the tax gap is important, in the U.S. and around the world. Tolerance of tax cheating only encourages more people to avoid paying their fair share.

Cracking down on tax cheats, at home and around the world, and closing the tax gap are about fairness — and, if successful, it will not only ease the tax burden on honest taxpayers, but will also help government budgets.