Methodology and sources

Every number the calculator relies on, where it comes from, and what the model deliberately does not try to answer.

How the estimate is produced

The engine simulates your loans month by month rather than applying a formula to an average. For each month it applies the plan's payment rule, accrues interest, applies any interest waiver or principal match, and carries the balance forward. Income-driven payments are recalculated each year from the tax return that plan would use, which is why payments lag your salary by a year or two.

Forgiveness is applied at the plan's qualifying payment count, and the estimated tax on forgiven balances uses the federal and state rates you enter. Totals are also expressed in today's dollars using the discount rate you set, so a payment in year 25 is not counted the same as one today.

No part of this calculation uses AI. The engine is ordinary arithmetic in ordinary code: the same inputs produce the same outputs every time, and any figure on the page can be traced back to a published rule. The optional AI explainer, if you switch it on, is given the results and asked to describe them; it is not consulted about what the results should be, and it cannot change them.

The figures, and where they come from

Figure	Value used	Source
RAP payment	1%–10% of AGI by bracket, $10/month minimum, minus $50 per dependent	One Big Beautiful Bill Act, as implemented by ED
RAP interest waiver and principal match	Unpaid interest waived; principal falls by at least the payment, up to $50	Same
RAP forgiveness	After 360 qualifying payments, taxable as income	Same
IBR	10% of discretionary income over 20 years; 15% over 25 years for pre-2014 borrowers; loans before 7/1/2026 only	Higher Education Act as amended
Poverty guideline	$15,960 base plus $5,680 per additional person, 48 states and DC	HHS 2026 poverty guidelines
Professional borrowing limits	$50,000 a year, $200,000 aggregate; Grad PLUS closed to new borrowers 7/1/2026; 3-year legacy window	One Big Beautiful Bill Act
PSLF	120 qualifying payments, 30 hours a week minimum, forgiveness tax-free federally	34 CFR 685.219 and ED guidance
Autopay discount	1.0% through 6/30/2028 for borrowers enrolled by 9/30/2026, then 0.25%	ED servicing guidance
Retirement and HSA limits	$24,500 elective deferral; $4,400 self / $8,750 family HSA	IRS 2026 limits

What the model does not cover

RAP's spousal-loan offset for joint filers.
State taxation of PSLF beyond a single on/off setting.
Future changes to federal rules, tax brackets or interest rates.
Institutional aid, service scholarships and grant eligibility.
Anything specific to your tax situation, which is what a CPA is for.

Official sources

Corrections

If you believe a figure or a rule here is wrong, write to partner@xocaliber.io with the source. Corrections are made promptly and the review date is updated.

Report a correction

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