SimpleKit Housing Tools

Mortgage calculator with extra payments

See your payment, amortization timeline, and total interest clearly, then test how weekly timing, recurring extras, and lump sums change the result.

Built to answer the practical questions most people actually have: What will my payment be, how much interest will I pay, and is adding a little extra worth it?

Start the calculator How mortgage amortization works
No login Runs in your browser Built for quick scenario testing

Built for clarity

A practical calculator for real mortgage decisions

Use it to compare payment frequencies, preview your renewal balance, and see whether extra payments meaningfully change your total interest cost.

Baseline view Regular payment

Payment amount, interest cost, and full payoff timeline.

Scenario view Extra-payment impact

Recurring extras and lump-sum prepayments modeled side by side.

Renewal view Term-end balance

Useful for understanding where you stand after a 1, 3, 5, or 10 year term.

Calculator

Build your mortgage scenario

Start with the core numbers first. Open the extras section only if you want to test faster payoff strategies.

Quick answer first

Start with the four core mortgage inputs. Open the other sections only if you want to refine the scenario.

Quick answer

Core mortgage inputs

Use these to get your payment and payoff timeline immediately.

Derived mortgage amount $0

This becomes the mortgage principal used in the calculations.

Improve your payoff Optional extra payments

Add a little to every payment

Useful when you want to see whether a small recurring extra makes a meaningful difference.

Plan one-time prepayments

Model larger one-off payments by amount and month from the mortgage start date.

Refine assumptions Optional deeper settings
See the mortgage breakdown

Actions

Save or share this scenario

Use these after you are happy with the result.

Visuals

See the payoff curve, not just the totals

These charts make it easier to see how principal falls over time and how interest changes when you pay faster.

Amortization

Yearly summary and payment-level detail

Start with the yearly summary for readability, then open the payment-level table if you want a deeper audit trail.

Compare frequencies

How each payment cadence changes the shape of the mortgage

Most people only need one quick insight first. Open the full comparison only if you want to compare every schedule side by side.

Compare all payment schedules

Next question

Pay down faster or invest instead?

This is an optional planning handoff once you already like the mortgage scenario above.

Open the mortgage-versus-investing handoff

Learn

Helpful mortgage notes in plain English

Use these notes as a quick guide when you are deciding whether to change frequency, add extras, or focus on your next term renewal.

What amortization really means

The amortization period is the full payoff timeline used to calculate your required payment. It is not the same as your mortgage term. A 25-year amortization with a 5-year term still leaves a balance to renew after year five.

Why payment frequency matters

Changing frequency can affect how often principal gets reduced. Accelerated weekly and accelerated bi-weekly schedules usually help the most because they effectively add the equivalent of one extra monthly payment each year.

Why extra payments have leverage

Mortgage interest is charged on the remaining balance. When you reduce principal earlier, every later interest calculation starts from a smaller number. That is why even small recurring extras can save meaningful interest over time.

How lump sums help

A lump-sum prepayment creates a one-time jump downward in your balance. That can be especially helpful near the start of the mortgage, when a larger share of each regular payment is still going toward interest.

Methodology

Assumptions used in this calculator

Mortgage conventions vary between lenders, so this section makes the modeling choices visible instead of hiding them.