2017 MA Child Support Calculator

September 15, 2017 Massachusetts Child Support Calculator

This Child Support Calculator uses the September 15, 2017 Massachusetts Child Support Guidelines, which were required for child support orders in MA made between September 15, 2017 and June 14, 2018. The state changed some formulas for calculating Child Support starting June 15, 2018, so all new child support calculations should use the June 15, 2018 MA Child Support Calculator.

Attorney Rueschemeyer provides expert divorce mediation for Worcester, Boston, Springfield, and all MA locations with online divorce mediation on Zoom. Please feel free to contact Attorney Julia Rueschemeyer with any questions you have about divorce mediation and uncontested divorce.

To calculate how much child support you should pay or receive for court hearings between September 15, 2017 and June 14, 2018, simply:

  • a) Enter a name for yourself and your spouse (fake names are fine)
  • b) Enter the number of children under age 18 that you have together
  • c) Enter the number of children you have together who i) have turned 18 but not yet turned 23 and ii) live with you or are supported by you. If a child is still attending high school, treat the child as under 18.
  • d) Indicate the amount of time that the child spends with each parent by choosing from among 3 choices: about 50% time with each parent, about 1/3 of the time with you and 2/3 of the time with your spouse, or about 2/3 of the time with you and 1/3 of the time with your spouse. Choose the one that is closest to your situation.
  • e) Enter:
    i) gross weekly income for each spouse,
    ii) the weekly amount paid by each spouse for childcare,
    iii) the amount paid by each spouse for family or individual health care insurance each week,
    iv) the amount paid weekly by each spouse toward the CHILD’s vision or dental insurance, and
    v) the amount each spouse pays out weekly for alimony or child support from a previous relationship or marriage.

If you are interested in how current Massachusetts child support calculations compare to calculations from before September 15, 2017, you can use this older calculator based on August 2013 Child Guidelines. If you need to divide a defined benefit pension–the kind of pension that many school teachers, state employees, and federal employees have–you can use this $35 present value pension calculator.

Preliminary evaluation of the June 15, 2018 Massachusetts Child Support Guidelines Worksheet

Posted by Professor Benjamin Bailey, May 23, 2018

Bottom Line: The June 15, 2018 Child Support Guidelines Worksheet represents a huge improvement over the September 15, 2017 Worksheet, but in 50-50 parenting time cases, it fails to share health care, childcare, and dental/vision costs in a transparent, fair, or reasonable way.

Improvements in the June 15, 2018 Worksheet:

1) It adjusts the numbers in Table B so that child support numbers in cases that involve both under-18 and over-18 children at the same time are near enough to correct.

2) It does calculations for 50-50 parenting time cases on a single, calculating worksheet, which is a huge practical improvement over the older worksheets (which required the use of two calculation sheets and an additional manual arithmetic step).

Failures in the June 15, 2018 Worksheet:

1) The layout and instructions in the new Section 1 (“Age, Number, and Parenting of Children”) are so convoluted that many people who are not already familiar with MA child support calculations will struggle to use the worksheet correctly.

2) In cases of 50-50 parenting time (and the rare “split” parenting arrangement), the new June 15, 2018 Worksheet is unable to account for health care, childcare, and dental/vision costs in a transparent or reasonable way. This is not a new problem. As will be discussed below, both the 2013 and the 2017 Worksheets also failed to handle these costs in a way that made sense.  For a transparent, sensible way of sharing these costs, see the MA Deviation Child Support Calculator.


In 50-50 Parenting Time Cases, the 2018 Child Support Guidelines Worksheet fails to share health care, childcare, and dental/vision costs in a transparent or reasonable way.

Take the example of a couple who have one child, identical incomes ($2500/week), and 50-50 custody. In this case, the worksheet gives a child support amount of $0, which is intuitively and logically correct.

If Spouse A pays $100/week for health care and childcare, it is similarly obvious how this cost SHOULD be shared: they have equal incomes and equal custody, so they should equally share the $100/week for health and child care costs. This would mean Spouse B should reimburse Spouse A $50/week, so that each is contributing $50/week.

When this scenario is run through the 2018 Child Support Guidelines Worksheet, however, the spouse who pays the $100 per week for health care is only reimbursed $18 rather than the $50. So one spouse pays 82% of the health care costs and the other pays only 18%, even though they have exactly equal incomes and exactly equal parenting time. In this case the person who happens to write the check for health care or childcare expenses is punished financially.

Failure to account for these costs in a reasonable way in 50-50 cases is not a new problem. When this same scenario–equal custody and equal incomes of $2500–is run through the September 15, 2017 Worksheet, the person who pays $100 for health gets $118 from the other spouse. So one spouse makes a profit of $18 and the other spouse pays $118 for health care that only costs $100!

When this scenario is run through the 2013 Child Support Guidelines Worksheet, one spouse pays $84 and the other pays $16 (rather than the appropriate $50 each).

In the scenario of equal income and 50-50 custody described above, the June 15, 2018 Worksheet financially punishes the spouse who happens to write the check for health care or childcare. In other 50-50 scenarios, however, the person who writes the check is rewarded for doing it.

For example, in a 50-50 case where Spouse2500 makes $2500 per week and Spouse1000 makes $1000 per week, the child support payment is $272, assuming no one pays any health care or childcare costs.

If Spouse2500 writes the check for $100/week in health care costs, the child support amount changes to $235, which means Spouse1000 is covering $37 of the $100 and Spouse2500 is covering $63.

If you switch who is writing the check for the health care insurance, the numbers shift. If Spouse1000 writes the check for health care insurance, the child support amount goes up $82 from the no-health-insurance child support figure. Now Spouse2500 is covering $82 of the $100 health care cost and Spouse1000 is only paying $18 of it.

Child support numbers should be based on income, not who happens to write the check to the child care provider or to the health insurance company. If you would like to share health care and childcare costs in a way that is fair and transparent, and in which the numbers don’t jump around based on who happens to write the check, you can try the MA Deviation Child Support Calculator on this site.

The 2017 Massachusetts Child Support Guidelines Fail Math:

The September 15, 2017 State Child Support Guidelines Worksheet generates the wrong outcomes in all calculations
that include children under-18 and over-18 at the same time

Posted by Professor Benjamin Bailey, September 18, 2017
[email protected]

If you appreciate the work I have done here, I ask that you add a link to this page on your blog, website, or article.

The 2016-2017 Child Support Guidelines Task Force modified Massachusetts child support laws. One modification specified that the amount of child support for many eligible children between 18 and 22 should be reduced by 25%. Unfortunately, the economic consultants hired by the Task Force failed to do the high school level math correctly, and they created a table of numbers to use in child support calculations in which half of the numbers are wrong.

This means that as of September 15, 2017, every child support calculation that involves a) at least one child under 18 AND b) at least one child over 18 will give wrong results, resulting in lower child support payments than the Task Force intended. These errors are most obvious in cases where adding an additional child to the calculator LOWERS your overall support. The Task Force intended for additional children over 18 to increase overall child support, but to increase it by less than it would increase by adding a child under age 18. Instead, in four cases, it actually LOWERS the overall child support award.

The guideline child support amounts are only correct in cases where all the children are under 18, or when all the children are over 18. If both kinds of children-over 18 and under 18-are put into the Child Support Guideline Worksheet at the same time, the presumptive child support outcomes are wrong.

If you would like to see this for yourself, run the following 3 family scenarios through the 2017 Massachusetts CHILD SUPPORT GUIDELINES WORKSHEET. The parents’ income stays the same in all three families, and there are 3 children under 18, who remain constant, in all three families. In Family B, a child over 18 is added to the existing 3 children under 18. In Family C, two children over 18 are added to the existing 3 children. Adding children results in actual, total child support decreasing, from $538 in Family A with 3 children, to $531 in Family B with 4 children, and $519 in Family C with 5 children.

  • Family A:

    Number of Children:
    3 children under 18 0 children 18-23 Income (same in all 3 families):
    Recipient income is $500/week;
    Payor income is $2000/week

    Result: $538 week presumptive child support payment

  • Family B:

    Number of Children:
    3 children under 18 add 1 child 18-23 Income (same in all 3 families):
    Recipient income is $500/week;
    Payor income is $2000/week

    Result: $531 week presumptive child support payment

  • Family C:

    Number of Children:
    add 2 children 18-23 0 children 18-23 Income (same in all 3 scenarios):
    Recipient income is $500/week;
    Payor income is $2000/week

    Result: $519 week presumptive child support payment

As you can see, adding more children DECREASES the amount of child support ordered. This is a math error. It was not the intention of the Task Force, as described in their actual  CHILD SUPPORT GUIDELINES document.

Where does the error come from?

The errors all come from having the wrong numbers in “TABLE B: ADJUSTMENT FOR NUMBER AND AGES OF CHILDREN,”a table at the bottom of the CHILD SUPPORT GUIDELINES WORKSHEET, which looks like this:

The erroneous numbers are introduced into the Worksheet at Line 3.c “Adjustment for number and ages of children covered by this order.” A smaller number in this spot in the Worksheet results in a lower presumptive child support amount, and a larger number results in a larger presumptive child support amount. All of the erroneous numbers in Table B are too small, resulting in presumptive child support numbers that are too small.

This table with errors was created on pp. 20-21 of a document called Economic Review of the Massachusetts Child Support Guidelines, 2016-7, which was created by economic consulting groups. (I wonder how much they were paid?) I will explain where their logic and math went wrong in the section below.

First, note that the first column (from 1.00 to 1.48) and the first row (from .75 to 1.11) ARE correct. It is only the numbers that result from combining children both over-18 and under-18 that are incorrect.

Even cursory examination of Table B shows that the numbers don’t make sense. As you can see, numbers in the first row grow larger as you move to the right, and numbers in the first column grown larger as you move down. This makes sense, because as you have more children, child support payments increase. But if you look at the rows that start with 1.25, 1.38, and 1.45, the numbers start going down when you add more children!!

A more complicated way to see it is to think about how much you get for adding a child. If you have one child under 18, you get “1”. If you have two children under 18, you get “1.25”, which is 25% more. So adding a second child (under 18), gets you 25% more than you would get for just having one child.

If you have a child under 18 and you add a child over 18, you should get almost as much as for having 2 children under 18. You should get exactly 25% less for adding the child over 18 than you would get for adding a child under 18. This means you should get 75% of the “under-18-second-child-increase”. In other words, you should get 75% of .25 (this is the standard increase for a second child–see below), which is .1875, rounded to .19. So the number in Table B for 1 child under 18 with 1 child over 18 should be 1.19, in the spot where the current table has an erroneous 1.09.

What should the numbers in Table B look like?

The numbers for Table B are not hard to calculate. I have not had math since high school, but I was able to put formulas into a spreadsheet and generate the correct numbers in about 15 minutes. (Did I ask already, how much the economic consultants got paid?)

The correct numbers for Table B should look like this

As you can see with even a quick scan, the numbers always go up if you move to the right across a row. In other words, you always get more child support if you have more children, even if you only get a little more for adding a 4th or 5th child. This is the intention of the child support law.

A little explanation of the logic and math:

Child support does not double for having two children instead of one, or triple for having three children instead of one. Child support increases by legally set, fixed percentages that decrease for each successive child. Assuming the children are under 18, it increases by 25% for a second child; 10% for a third child; 5% for a fourth child, and just 2% for a fifth child. These rates of increase have been set by law since at least August 2013.

The 2017 law specifies that children over 18 should count for 25% less than younger children in child support calculations. Thus if one moves from 1 child under 18 (which generates “1”in Table B), to 1 child under-18 PLUS 1 child over-18, one simply has to add 75% of the normal 25% increase one gets for a second child. If one has 2 children under 18 (which generates “1.25” in Table B) and one adds a third child, over 18, one simply adds 75% of the normal 10% increase that one gets for a third child.

You can see these formulas by downloading the spreadsheet here that I used to make these Table B calculations.

[Added on October 11-13:
The economic consultants did not understand the implications of the fact that the intervals between 0 and 1 children, 1 and 2 children, 2 and 3 children, etc. were not identical. The formula they used to generate their (erroneous) Table B would only work if the increase for each child (under 18) from 0 to 5 were exactly the same, i.e., if a second child doubled the child support amount, a third child tripled it, a fourth child quadrupled it. For their formula to work, the increase from 0 children to 1 child would ALSO have to match the interval from 1 to 2 children, 2 to 3 children, etc.

The economic consultants’ explanations and sample calculations on pp. 20-21 of their Economic Review document show how they arrived at the wrong numbers for Table B. Instead of adding discounted increments for children over 18, as I have done, they tried to discount backward from the numbers in column 1, which are the multipliers for children under 18. This led them to discount children under 18 in every single calculation that involved a mix of children over and under 18. There is no situation in which children under 18 should have their child support number discounted.

In the example they give on p. 21, for 1 child under-18 and 1 child over-18, they discount the “1.25” that one gets for 2 children under 18. They do this by multiplying it by .875, a discount of 12.5%. (This results in their erroneous 1.09.) They write, “Conceptually, it reduces the increase for a second child by 12.5 percent (one-half of the 25% discount decided by the Task Force) because one of the two children is 18 or older.” This makes two major conceptual errors. First, there is no need to discount an increase for an over 18 child by 12.5%–the Guidelines are clear that the increase should be discounted by 25%. Second, they confuse the increase for a second child with the total child support number for two children. The “1.25” for 2 children is NOT an increase. One child gets “1”. The increase for a second child is “.25”, resulting in “1.25” for two young children. These two conceptual errors lead them to discount both the increase (“.25”, a small number, which should be discounted) and the base number for children under 18 (“1”, a large number, which should NOT be discounted). This is what leads to numbers that are too low in every case. To give a poor, mixed metaphor, they discount the bathwater (children over 18), and then they discount the whole baby (children under 18) too!]

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More errors, discovered by others, in the Child Support Guidelines Worksheet and Task Force

Posted by Professor Benjamin Bailey 10/4/2017

Gabriel Cheong reports a calculation bug in the Child Support Guidelines Worksheet. If the numbers in lines 4d and 4e are opposites of each other (e.g. 50 and -50; or 13 and -13; or 43 and -43), the logic in the calculator fails at line 4g and enters a “0” instead of a positive value of 4d or 4e. Line 4g specifies: “If 4(d) is < $0, enter the positive value of 4(d) or 4(e), whichever is less; otherwise enter zero”. When the positive values of 4d and 4e are the SAME, such that one is not LESS than the other, the calculator thus returns a “0” . This problem will occur relatively rarely, but it can have large consequences, e.g., nearly $3000/year in Cheong’s example. The calculator of Attorney Julia Rueschemeyer, at the top of this page, does NOT make this error.


A problem that will affect many more people is the double-weighting of expenses entered under 2b-2d in cases of 50-50 custody. In cases of shared custody, a person who pays medical/dental/vision/childcare, can actually PROFIT from those payments. This problem was first reported on September 20 by Michael Freedman in a comment at the bottom of the page of a Skylark blog post. As Freedman illustrates, in a shared custody case, a person who pays $100 for a child’s medical expenses, can be paid back $118 for that expense! This issue is discussed at greater length in a blog post by by Jason Owens. In brief, the Task Force did not want relatively high childcare and health costs to overly affect child support child support payments that are otherwise based largely on difference in income between spouses, so they limited the effect of such childcare and health payments to an adjustment of 15% of a given child support figure (See Section II.E. of Report of the Task Force for the 2016-2017 Quadrennial Review of the Massachusetts Child Support Guidelines). As Freedman points out, however, in shared custody situations, this 15% limit is applied twice, through cross-guidelines:

“I have recently reviewed the new CS guidelines and have found what I believe to be an oversight in how the health care cost is shared between parties in the case where custody is shared equally. When calculating first with the recipient paying health care, the 15% rule is applied to a large order because it is for sole custody and the recipient’s order grows to accommodate that. Then the roles are reversed and the payor now pays the health care. The 15% rule is again applied to a large order because it is for sole custody and the payors order is decreased by that larger number. Then when you take the difference between the two orders, the one who pays the health care is benefited by potentially a 30% offset in their favor. But that 30% is based on a sole custody order, not the actual order that would result from taking the difference in orders without the health care taken into account.”

Coverage of these issues in Massachusetts Lawyers Weekly

Problems with the implementation of the new 2017 Child Support Guidelines are discussed in an October 19 article by Kris Olson in Massachusetts Lawyers Weekly.