FinToolSuite

Save vs Pay Off Debt Calculator

Updated April 17, 2026 · Savings · Educational use only ·

Should extra cash go to savings or debt?

Compare expected savings growth against interest saved by paying off debt to decide which option wins. Enter extra cash and see the result instantly.

What this tool does

Enter monthly extra cash, savings return, debt rate, and horizon. The tool compares the two paths.


Enter Values

Formula Used
Monthly payment
Savings monthly return
Debt monthly rate

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Disclaimer

Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.

The rule of thumb is mostly right: pay debt above your expected savings return, save otherwise. 300/month at 22% debt rate vs 5% savings return: pay the debt. At 6% debt vs 7% savings return: save — but the gap is small and debt-free feels better. This tool shows the cash gap across your horizon to decide.

Decision comparator.

Quick example

With monthly extra cash of 300 and expected savings return of 5% (plus debt interest rate of 8% and horizon of 10), the result is 8,299.13. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.

Which inputs matter most

You enter Monthly Extra Cash, Expected Savings Return, Debt Interest Rate, and Horizon. Two inputs usually tip the answer one way or the other. Identify which ones matter most by flipping each value past a round threshold and watching whether the winning option changes.

What's happening under the hood

Future value of the same monthly amount at savings rate vs debt rate. the upper tax rate wins — debt saving compounds at the debt rate. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.

Why the number matters

Saving without a target is like driving without a destination — you'll make progress, but you won't know when you've arrived. This tool gives you a concrete figure to work toward, which is the first step in turning a vague intention into an actual plan.

What this doesn't capture

The calculation assumes a steady savings rate and a stable interest rate. Real saving journeys include emergencies, windfalls, and rate changes — especially in easy-access products. The figure is a direction of travel, not a guarantee.

Example Scenario

Save vs debt produces a winner based on the inputs provided.

Inputs

Monthly Extra Cash:300 £
Expected Savings Return:5
Debt Interest Rate:8
Horizon:10
Expected Result£8,299.13

This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.

Sources & Methodology

Methodology

Future value of the same monthly amount at savings rate vs debt rate. the upper tax rate wins — debt saving compounds at the debt rate.

Frequently Asked Questions

When does saving beat paying debt?
When expected savings return exceeds the debt rate. For mortgage (4-6%) and index funds (7%+), saving wins. For credit cards (20%+), debt always wins.
Does psychological benefit matter?
Yes. Debt-free feels different from owning assets that offset debt. Many people pay down mortgage despite the maths slightly favouring investing.
What about emergency fund?
Build a small one first (1k-2k). Then you can attack debt without panicking over emergencies. Full emergency fund comes after high-rate debt is cleared.
Tax-advantaged accounts change this?
Yes. Pension match makes saving beat almost any debt. tax-advantaged savings account tax-free returns lift savings return somewhat. Include tax advantages in the savings return you enter.

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