The penalty is calculated based on each month the tax return is late multiplied by each shareholder or partner. So a business tax return with no tax due, filed the day after the March 15th due date, could cost a married couple who jointly own an S corporation $490 in penalties! Take action Here are some ideas to help you avoid penalties: File on time. If your entity cannot file your tax return in time, consider an extension. Do not file your Form 1040 tax return until you receive all your K-1s from