MoveMath gives a household one bedroom for the adults plus one bedroom for every two children, up to four bedrooms. Two adults with two children need two bedrooms; with three children, three. The rule follows HUD’s two-persons-per-bedroom guidance, and it decides which HUD Fair Market Rent each budget uses. In New York, going from two to three bedrooms adds $789 a month.
Bedrooms by household
| Adults | Children | Bedrooms |
|---|---|---|
| 1 | 0 | 1 |
| 1 | 1 | 2 |
| 1 | 2 | 2 |
| 1 | 3 | 3 |
| 2 | 0 | 1 |
| 2 | 1 | 2 |
| 2 | 2 | 2 |
| 2 | 3 | 3 |
| 2 | 4 | 3 |
| 2 | 5 or more | 4 (largest Fair Market Rent size) |
The formula is 1 + (children ÷ 2, rounded up), capped at 4. A single adult or a couple counts as one bedroom; MoveMath models households of one or two adults.
Where the rule comes from
Voucher subsidy standards. HUD’s regulation for Housing Choice Vouchers, 24 CFR 982.402, tells each housing agency to set standards that provide “the smallest number of bedrooms needed to house a family without overcrowding.” A single person gets a studio or one-bedroom. Agencies may grant exceptions “justified by the age, sex, health, handicap, or relationship of family members.” The regulation itself does not fix a persons-per-bedroom number.
Fair housing occupancy guidance. HUD’s 1998 statement of policy (63 FR 70256) adopted the 1991 Keating memorandum, which says “an occupancy policy of two persons in a bedroom, as a general rule, is reasonable under the Fair Housing Act.” The memo treats that as rebuttable: room sizes, children’s ages and local codes all matter.
MoveMath applies two persons per bedroom with the adults in their own room. It is a minimum, not a recommendation; you can override the bedroom count in every calculator.
What each extra bedroom costs
HUD Fiscal Year 2027 Fair Market Rents (40th-percentile gross rent, utilities included):
| Metro | 1-BR | 2-BR | 3-BR | 4-BR | 2 → 3 BR |
|---|---|---|---|---|---|
| New York, NY-NJ | $2,729 | $2,971 | $3,760 | $4,121 | +$789/mo |
| Chicago, IL-IN | $1,780 | $2,011 | $2,586 | $2,954 | +$575/mo |
| Phoenix, AZ | $1,493 | $1,734 | $2,287 | $2,537 | +$553/mo |
| Nashville, TN | $1,650 | $1,798 | $2,309 | $2,799 | +$511/mo |
| Austin, TX | $1,530 | $1,817 | $2,292 | $2,689 | +$475/mo |
| Dallas, TX | $1,536 | $1,807 | $2,275 | $2,892 | +$468/mo |
Source: HUD FY2027 Fair Market Rents (91 FR 56156), principal county of each metro.
The step from two to three bedrooms is the largest in five of these six metros (Dallas’s three-to-four step is bigger), partly because HUD adds 8.7% to three-bedroom and 7.7% to four-bedroom Fair Market Rents to help larger families find units, according to the FY2027 notice.
What the extra room does to a family budget
For two adults with a preschooler and a school-age child on $120,000 (center-based childcare, two cars, 2026 taxes):
| Metro | Left over with 2 bedrooms | With 3 bedrooms | Yearly cost of the third bedroom |
|---|---|---|---|
| Nashville, TN | $38,211 | $32,079 | $6,132 |
| New York, NY-NJ | −$5,206 | −$14,674 | $9,468 |
Try your own case in the relocation budget planner or compare the income each size needs with the rent affordability calculator.
Common situations
Couple expecting a first child. One bedroom before the birth, two after: MoveMath counts any child, including an infant, toward the children’s rooms.
Single parent with two children. Two bedrooms under the rule — one for the parent, one shared by the children. If you want separate rooms for older children, the three-bedroom rent above shows the cost.
Two children of different sexes. The rule lets them share. Housing agencies and landlords may set different standards, and your family may prefer separate rooms.
A grandparent or other adult moving in. MoveMath’s calculators model one or two adults. For a third adult who needs a room, set the bedroom count by hand.
A home office. Override the bedroom count to add a room and see what it costs each month.
Family budgets for every metro, with the bedroom count chosen automatically, are on pages such as Austin and Nashville.