Welcome to Math4Law

Do you need to calculate interest on arrears? Having trouble determining the interest on an irregular flow of charges and payments? Trying to figure out how to calculate interest on unpaid child support? Or maybe you need to calculate the present value of a future stream of payments so you can settle a divorce case?

Math4Law solves all these problems and more. This modern web application provides a set of user friendly tools that make every calculation quick, efficient, and error free. 

Interest Tracker

Use Interest Tracker to calculate interest on an irregular flow of charges and payments, such as past due child support, child support arrears, garnishments, debt collections, private loans, and business credit arrangements.

Interest Tracker Capabilities

  • Log charges and payments, auto calculate interest and balance on every transaction.
  • Interest Tracker files are stored in the cloud and are available to all account users.
  • Simple or Compound Interest.
  • Apply Payments in various ways (interest first, principal first).
  • Allow for grace period to meet your state law requirements (if applicable).
  • Save to PDF or print to any installed printer in a printer friendly format.
  • Email the calculation to your inbox or to any other email address.

Ready to give it a try? Start your free trial now. No credit card required!

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Other Calculators

  • Present Value Calculators
    • Pension Plan
    • Stream of Equal Payments
    • Stream of Increasing Payments (useful for cost-of-living adjustment)
    • Lump Sum needed presently to fund a stream of future payments
    • Maintenance Entitlement
    • Monthly Payment available from Lump Sum
  • Future Value Calculators
    • Stream of Equal Payments over time
    • Value of Lump Sum investment over time
  • Loan payments and terms
  • Save to PDF or print to any installed printer in a printer friendly format.
  • Email the calculation to your inbox or to any other email address.


  • Modern and responsive web application, works in every modern browser, such as Chrome, FireFox, Edge, Safari.
  • Available on Windows, Apple, and Android devices.
  • Works on every screen size, from large monitors to smartphones.
  • True multi-user environment for the Law Office. Add your staff to your account for no additional cost.

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Math4Law annual subscriptions cost as follows:

  1. Unlimited subscription – $119. This subscription includes unlimited interest calculation files, unlimited calculators use, and unlimited users.
  2. Basic subscription – $79. This subscription is appropriate for a small office and is limited to a single user and up to 3 active interest calculation files. You can always delete a file and create a new one instead, but you can only have up to 3 files at the same time.
  3. Personal subscription – $79. For personal use. Same limits as the basic subscription.

Math4Law can also be used on a per-file basis. If you only need to calculate interest from time to time and don’t need an annual subscription, you can pay per file. Create a free account to see the available options.

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Why Use Math4Law?

Calculating interest on an irregular flow of charges and payments is not a trivial task. You could use Excel for simple calculations, but the risk of mistakes is too high, it takes too long to maintain the spreadsheet, and you have to really know what you are doing. Math4Law takes the risk out of the equation, saves you time, and gives you the confidence that you got the right result.

Imagine that you need to submit a child support arrear calculation for a judgement. Which one will be treated more seriously, a printed Excel page or a formal Math4Law calculation? The Math4Law printed format is more credible, and is less likely to trigger questions about the accuracy of the calculation you provided.

In some states, child support arrears have special rules, such as compounding the interest, or allowing for a grace period before interest starts to accrue. Math4Law takes care of these complexities, and much more.

Create your account and give it a try today. No credit card required.

Start your free trial now


Math4Law is based on Legal Math, the desktop-based application that has been serving Law Offices for nearly 30 years. If you are looking for the desktop version, it is available here.