Compare one canonical monthly loan schedule with a proposed acceleration plan. Enter actual P&I when known, place a lump at an explicit monthly boundary, and distinguish interest benefit from the cash needed to obtain it.
Payment, maturity and event dates
The calculator separates an entered maturity assumption from the duration implied by an actual monthly principal-and-interest payment. If actual P&I is blank, it derives the original installment from the outstanding balance, annual note rate and remaining months. Escrow, insurance and other account charges are excluded. If an entered payment changes the implied payoff duration, the receipt shows the mismatch rather than confirming a lender maturity. An optional first due date anchors all payment labels to its original day. A January 31 anchor therefore reaches February 28 and then March 31 in 2026, rather than drifting permanently to the 28th. Month 0 represents the preceding monthly boundary before first-period interest. A future before-payment lump reduces principal before that month's interest posting and regular payment; an after-payment lump occurs afterward. These are equal-monthly modeling boundaries. They do not calculate arbitrary-day interest, guarantee that a servicer accepts a recast, or replace a current payoff quote. Leave dates blank when only relative payment months are known. The underlying unrounded schedule determines every result, chart, cash row and export.
Read the cash ledger before the savings
A lump is a commitment of principal, not money that becomes available because interest falls. The proposed plan includes every regular payment, applied lump and modeled charge. Requested lump cash is clipped to the debt remaining at the selected event; anything unused stays explicitly uncommitted. A lump scheduled after payoff is unused and creates no recast fee. The entered prepayment charge is modeled once as a percentage of starting balance when actual extra principal first occurs. An eligible recast fee is separate cash at the event and is charged only if a positive balance remains to recast. Full payoff is not a recast. Gross interest avoided compares the two interest totals, while net financing-cost benefit subtracts charges. For the zero-rate reference, a $12,000 balance over 12 months has a $1,000 baseline installment; another $1,000 monthly finishes in 6 payments with no interest benefit. It exchanges liquidity for earlier debt elimination. Inspect each period to see interest, regular payment, lump, charges and the corresponding ending debt. Displayed cents are rounded independently from the full-precision model.
Recast and a feasible target month
Term reduction keeps the original contractual principal-and-interest amount while extra principal can shorten the schedule. A recast instead calculates a new base installment after an eligible partial-balance lump using an explicit remaining maturity assumption. Leaving the recast maturity blank preserves the entered term assumption. A before-payment event can include the current installment in the remaining count; an after-payment event starts the revised base installment with the following month. Continued monthly extras may still shorten either plan. A shorter assumed recast maturity may increase the payment, and the receipt exposes any resulting increase in the common cash budget. The target planner searches the canonical schedule for the least feasible cent-denominated monthly extra, rather than using a separate closed-form estimate that ignores events. It shows the required total monthly P&I budget and does not apply a recommendation exceeding an entered limit. Editing assumptions clears the old recommendation. The monthly-equivalent shortcut spreads one contractual installment over twelve months; it is not an annual lump or a biweekly payment service. Check eligibility, fees and actual payment handling with the lender.
Use one cash horizon for the optional investment
The investment illustration is separate from the loan's contractual interest comparison. Both strategies receive the same sufficient monthly cash budget through a common horizon covering both payoff paths. Both also receive the same cash available for the proposed lump and charges at their modeled before-interest or after-payment boundaries. One strategy uses that event cash to reduce debt and pay charges; the baseline invests it instead. Each path invests budget no longer needed for its regular loan payments, including cash released after payoff. A longer entered horizon must still cover both debt schedules. Requested cash that was never used remains a separate equal uncommitted amount, not fabricated investment growth. The entered return is an uncertain nominal annual rate after tax, compounded monthly; there is no additional tax deduction or risk adjustment. A negative net financing benefit remains negative even if the debt ends sooner. Review the assumptions and amounts before copying a Share link, since recipients can read those inputs. Device storage requires a separate Remember choice. CSV keeps raw USD and event ordering; Print presents the same modeled receipt and schedules.