Fidamen

Student Loan Payment Interest-Only Estimator

This estimator computes interest-only payments and related figures for student loan balances. It supports common options: interest-only period length, payment frequency, optional capitalization of unpaid interest, and a subsequent amortization phase.

Use the tool to compare the immediate cashflow benefit of interest-only payments against the longer-term cost if interest capitalizes or when amortization follows. Results are illustrative and depend on the inputs you provide.

Updated Nov 11, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 7d3f0d09fcb5 • Reviewed by Fidamen Standards Committee

Flexible mode: choose whether interest capitalizes and calculate the amortizing payment on either the original principal or capitalized balance. This is the default mode.

Inputs

Results

Updates as you type

Interest-only payment

$125.00

Total interest during interest-only period

$1,500.00

Principal after interest-only (may include capitalization)

$30,000.00

Post-interest amortizing payment (per period)

$318.20

OutputValueUnit
Interest-only payment$125.00USD
Total interest during interest-only period$1,500.00USD
Principal after interest-only (may include capitalization)$30,000.00USD
Post-interest amortizing payment (per period)$318.20USD
Primary result$125.00

Visualization

Methodology

Calculations use periodic-rate math: periodic_rate = annual_rate_pct / 100 / payments_per_year. Interest-only payment per period = principal × periodic_rate.

If interest capitalization is selected, accrued interest over the interest-only period is added to the principal before calculating amortizing payments. Amortizing payments use the standard fixed-payment formula for an installment loan with a constant periodic interest rate and fixed number of periods.

Worked examples

Example 1: $30,000 principal, 5% APR, 12-month interest-only period, monthly payments: periodic rate = 0.05/12 = 0.0041667. Interest-only payment ≈ $125.00 per month.

Example 2: Same loan but unpaid interest capitalizes at end of 12 months. Total interest ≈ $1,500; new principal ≈ $31,500; amortizing payments will be higher than if interest had been paid.

F.A.Q.

Is this calculator exact for my loan?

This tool provides modeled results using standard financial formulas. Actual loan servicing rules (grace periods, rounding, accrual conventions, or special capitalization timing) may differ. Always verify with your loan servicer for exact amounts.

What does capitalization mean?

Capitalization means unpaid interest is added to the loan principal, after which future interest accrues on the higher balance, increasing total interest costs and later payments.

Can I use different compounding than monthly?

You can approximate different compounding by changing 'Payments per year'. The calculator treats the periodic rate as annual_rate_pct / payments_per_year; it does not model intra-period compounding beyond that periodic rate.

How should I interpret the post-interest payment?

The 'post-interest amortizing payment' is the fixed payment per period required to fully repay the specified balance over the chosen amortization_period_months at the same periodic rate. If amortization_period_months is small, payments will be larger.

How accurate and secure is this tool?

Calculations use standard formulas but may be affected by input rounding and assumptions. For sensitive decisions consult your loan servicer or a qualified financial advisor. See citations for standards on software assurance and handling of financial computations.

Sources & citations

Further resources

External guidance

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: 7d3f0d09fcb5

What changed (latest)

v1.0.0 • 2025-11-11 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

UI

v1.0.0

Governance

Last updated: Nov 11, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

  • MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
  • MINOR: New features or fields that do not change existing outputs for the same inputs.
  • PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

  • Verify formulas and unit definitions against primary standards or datasets.
  • Run golden-case regression suite and edge-case suite.
  • Record reviewer sign-off with credentials and scope.
  • Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

  • Uses exact unit definitions from the Fidamen conversion library.
  • Internal calculations use double precision; display rounding follows the unit's configured decimal places.
  • Not a substitute for calibrated instruments in regulated contexts.
  • Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-11 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 175bd65fe9c2