Currently MaxiFi does not provide a specific Health Savings Account (HSA) feature, but here is how you handle HSA contributions in MaxiFi.
Contributions via salary reduction: Avoid both income tax and payroll tax
If you have a high deductible health plan and HSA through your employer, your employer is likely allowing you to contribute to your HSA pre-tax. This means that you end up not paying income taxes OR payroll taxes on this income. Employer contributions to an HSA are not considered income and so they're not subject to income tax or payroll tax. If the employee makes contributions by way of a salary reduction arrangement, those contributions are also not subject to income tax or payroll tax (see the instructions for IRS Form 8889; these contributions show up in Box 12, with Code W). When your HSA is pre-tax (no income tax and no payroll tax), reduce your gross income (your current/future earnings) that you report in MaiFi by the amount of your pre-tax contribution.
Contributions made outside your payroll system: Avoid income tax, but not payroll tax
If you use a bank or brokerage account other than the one your employer uses as an HSA custodian, you can send money to your HSA yourself, rather than using your employer's salary reduction plan. This may be your only option if your employer doesn't offer a means of contributing to an HSA via the payroll system. You won't have to pay income tax on that money, but you'll still pay Medicare and Social Security taxes on it (i.e. FICA tax). When you make your own HSA contributions (as opposed to using your employer's salary reduction arrangement) you make the contributions during the year with after-tax money, and then you get to deduct your contributions on your tax return regardless of whether you itemize deductions or take the standard deduction. But that just eliminates the income tax—there's no mechanism for recouping the payroll taxes you paid on that money. When your HSA avoids income tax but not payroll tax, you can enter the contributions you plan to make as Special Expenses that are excludable from AGI.
Using the HSA to pay medical expenses
For future withdrawals that are going to cover future medical expenses, you could enter the future withdrawals as Non-Taxable Special Receipts and the corresponding future medical expenses as Special Expenses. However, because those HSA withdrawals and medical expenses cancel each other out, you could simply not enter either one on the assumption that accumulated HSA funds will go to pay for future health expenses.