Loan & Mortgage Amortization Calculators

The loan/mortgage amortization landscape is almost entirely free — every major personal-finance media site and bank publishes calculators; OSS PTA tools (Beancount, hledger, Ledger) handle amortization natively. Spreadsheet templates remain the most flexible option. For the budget side see Actual Budget; for plain-text accounting see Beancount + Fava; for the household real-estate context see Household Real Estate & Mortgage; for the broader index see Self-Hosted Personal Apps; for FIRE projections see FIRE Projections; for inheritance see Inheritance & Tax Planning.

Free calculators (★)

• ★ BankRate — free; mortgage / auto / refi / personal-loan / amortization-schedule calculators; the most-comprehensive free set.
• ★ NerdWallet — free; calculators + comparison tables.
• ★ Calculator.net — free; bare-bones but accurate; lots of niche calculators (extra-payment, biweekly, ARM).
• ★ Mortgage Professor (Jack Guttentag) — free + paid; deep-dive mortgage analysis; "true cost" comparisons.
• Bogleheads wiki — "Mortgages" — free; deep math + tax-treatment notes. See Bogleheads & FI Education.
• Bankrate refi calculator — free; break-even on refinance fees vs rate savings.

Spreadsheet templates (★ flexible)

• ★ Google Sheets / Excel mortgage templates — free; the most flexible option; modify columns to model extra payments, biweekly, ARM resets, points, escrow.
• PMT, IPMT, PPMT, CUMIPMT, NPER — Excel functions; the canonical loan math primitives.
• vertex42.com — free templates; widely used.
• smartsheet.com / spreadsheetml.com — free templates.

OSS / programmatic

• ★ ledger / hledger amortization — free OSS; commands generate amortization schedules from a loan transaction. See Beancount + Fava.
• Beancount with Liabilities:Mortgage account — track principal-vs-interest split per payment; amortization schedule emerges from the ledger.
• GnuCash — free OSS desktop; loan-repayment calculator built in; auto-creates scheduled transactions.
• numpy / pandas — DIY in Python; financial functions: numpy.npv, numpy.irr, numpy_financial.pmt.
• R FinCal package — free OSS R; finance-math primitives.

Apps

• Mortgage Pro — free + paid; mobile.
• Karl's Mortgage Calculator — free; well-loved web calculator.
• Loan Calculator apps — many free; pick one with no ads / no data collection.

Mortgage-specific concepts to model

• ★ Amortization schedule — month-by-month split of principal vs interest.
• ★ Extra payment scenarios — $X/month extra, biweekly payments, lump sum at year N.
• ★ Points — paying points up-front to lower rate; break-even = points cost / monthly savings.
• ★ PMI / MIP — private mortgage insurance below 20% down; drops off automatically at 78% LTV (FHA differs).
• ★ Escrow — taxes + insurance bundled into payment; not technically loan amortization but lives in the same payment line.
• ★ ARM rate-reset — 5/1, 7/1, 10/1; need to model worst-case at cap.
• ★ Refinance break-even — closing costs / monthly savings; rule of thumb: stay in house > break-even months.
• Recast — fewer banks offer; lump-sum principal payment that re-amortizes the remaining schedule (vs prepay which keeps the schedule).
• Cash-out refi — replace mortgage at higher principal; pull out equity; tax considerations.

Auto loans

• Simple amortization — same math as mortgage; shorter terms.
• Pay extra principal early — same compound benefit; no prepayment penalty on most US auto loans.
• 0% financing vs cash-back tradeoff — calculate which beats; sometimes the cash-back > the interest cost.

Student loans (US)

• ★ studentaid.gov loan-simulator — free official tool; income-driven repayment plans (SAVE / PAYE / IBR / ICR), PSLF projection.
• ★ Mark Kantrowitz Student Loan Calculator (free, savingforcollege.com) — comprehensive.
• NerdWallet / BankRate — free comparison.
• PSLF (Public Service Loan Forgiveness) — track 120 qualifying payments; student aid portal.
• SAVE plan — income-driven; status changing 2024–26; check current state.

Personal loans / credit cards

• Snowball vs avalanche debt-payoff — calculator at unbury.us (free), undebt.it (free), Vertex42 spreadsheets.
• Debt-snowball/avalanche apps — many free; pick one.
• 0% balance-transfer math — break-even = transfer fee / months at 0%; avalanche if you can pay off before reset.

HELOC / home equity

• ★ Variable-rate HELOC — typically prime + margin; model rate-rise scenarios (especially relevant 2022–24 era).
• Fixed-rate home equity loan — second-lien fixed; standard amortization.
• Cash-out refi vs HELOC vs home equity loan — three different tools; model break-evens.

Refinance heuristics

• ★ Break-even months = closing costs / monthly savings.
• ★ Stay in house > break-even and rate drop > ~0.5–0.75% generally pencils out.
• ★ No-cost refi is rarely actually no-cost — fees are baked into the higher rate.
• ★ Recast is cheap (~$200–400) and sometimes a better answer than refi if rates have risen.

License / pricing

• BankRate, NerdWallet, Calculator.net, Mortgage Professor (free articles), Bogleheads, vertex42, smartsheet, Karl's Mortgage Calculator, studentaid.gov, savingforcollege.com, unbury.us, undebt.it: free.
• Mortgage Pro app: free + paid.
• ledger, hledger, Beancount, GnuCash, numpy, R FinCal: free OSS.
• Excel: paid.
• Google Sheets: free.

Pick this if…

• Default free quick mortgage calc: BankRate or Calculator.net.
• Want flexibility / what-ifs: Google Sheets template (vertex42).
• Already on plain-text accounting: Beancount / hledger native amortization.
• GnuCash user: built-in loan-repayment calculator.
• Considering refi or recast: Mortgage Professor for the deep dive + spreadsheet for break-even.
• Student loan strategy (US): studentaid.gov simulator.
• Debt payoff: unbury.us or a snowball/avalanche app.
• HELOC under variable rates: spreadsheet with worst-case rate scenarios.