Top Democrats in the Massachusetts Senate are seeking to boost state spending by more than 6% next year. Despite that increase, they say non-negotiable rising costs left them little wiggle room in crafting their budget.

The $61 billion budget plan unveiled Tuesday by Senate leaders is slightly smaller than the version already passed by the House, and diverges from it in areas like transportation funding and vocational school admissions policies.

Senate budget chief Michael Rodrigues said 65% of the new spending is in MassHealth, the state’s Medicaid and children’s health insurance program.

“Think nursing homes, long-term care for seniors,” the Westport Democrat said. “Think health care for seniors, for disabled, for low-income individuals. That’s the driver.”

The budget’s other main cost drivers are also fixed expenses, Rodrigues said, including other health and human services cost increases, insurance for public employees, and funding boosts for local schools required under a 2019 state law.

After accounting for those costs, all other spending increases total up to $59 million, or 0.1% of the total budget, he said.

“There’s very little, unless we want to slash services and programs that we provide to our citizens, more that we can do in any of these line items,” Rodrigues said.

Like the House budget that passed overwhelmingly last month, the Senate budget does not raise taxes to back up that 6% in growth. It’s built around a revenue estimate that includes almost $2 billion in education and transportation funding from the state’s millionaire’s tax, and $16 billion in reimbursements from the federal government.

Massachusetts is due to have a state budget in place by July 1, when the new fiscal year begins. The potential for major federal funding cuts looms as a major question mark over Beacon Hill, especially when it comes to potential changes to Medicaid.

Rodrigues said he’s heard from some experts that President Donald Trump might avoid Medicaid cuts because of the impact on red states, while others caution that anything could happen. He said lawmakers decided “to move forward and pass a budget based upon facts that we know now,” and reopen the spending plan later in the year if necessary.

“If they make significant reductions in Medicaid reimbursement, all bets are off,” Rodrigues told reporters. “Because that is close to over a billion dollars a month, I think, in MassHealth reimbursements to the commonwealth of Massachusetts.”

While the possibility of federal funding cuts could force the state to make reductions of its own down the line, Rodrigues said senators decided to “move forward and to pass a budget based upon facts that we know now.”

“We’ve just got to stay calm, stay focused and be open-minded enough that we might be back at the table in a few months,” he said.

In broad strokes, Senate President Karen Spilka said her chamber’s budget invests in mental health, child care and “regional equity,” including what she described as record levels of funding for regional transit authorities.

After this year’s budget included money for those transit authorities to eliminate fares for their service, the Senate’s budget for next year proposes to make write fare-free service permanently into state law. That requirement would be backed up with $40 million.

The two branches diverge on vocational-technical high school admissions. The state Board of Elementary and Secondary Education is slated to vote later this month on new regulations that would implement lottery-based admissions, instead of systems that use criteria like grades and attendance. The House budget would put that shift on hold while a task force studies admissions policies. But senators dropped that measure from their version of the budget.

The governor, the House and the Senate all included language in their budgets to put new limits on the broker fees charged in apartment rentals, as a way to take a bite out of the high cost of housing in the region. Those fees, often one month’s rent, are currently an added cost for many tenants moving into a new apartment.

The House and Senate bills both seek to make the person who hires the broker, usually the landlord, responsible for those fees.

Rodrigues said the Senate opted not to mirror the House’s approach, which leaves room for the tenant to still be on the hook for the fee if they “initiated contact” with the real estate agent, including by “responding to an advertisement or listing.”

“We think our language accomplishes what we want it to accomplish: that there be no broker fees onto tenants,” Rodrigues said.

After the Senate passes its budget this month, the debate will move to closed-door talks between a team of three state representatives and three senators tasked with crafting a compromise bill. Massachusetts has not met its own deadline of a July 1 finalized budget in many years: the governor typically signs the budget in late July or early August, giving the commonwealth the frequent honor of being the last state to finish its budget.