Calculator
Prepay Break-Even Calculator
A prepay discount is only a discount if you use the whole term. Stop halfway and you have paid a lump sum for cycles you never took — which can leave you worse off than the month-to-month price you were avoiding. Enter the lump sum, the cycles it buys, and the provider's own no-commitment rate, and see the cycle where the deal turns.
Calculator
What actually leaves your account when you take the prepay offer — the whole figure, not the per-month rate the page prints beside it.
How many cycles that lump sum buys — 3 for a three-month prepay, 12 for a year. Must be a whole number; you cannot buy half a cycle.
What one cycle costs with no commitment, from the provider's own terms. This is the number the prepay is being compared against, and the one most pages bury.
Enter the lump sum, the whole number of cycles it covers, and the provider's own no-commitment price. Without that third figure there is nothing to break even against, and the discount cannot be checked at all.
Why the amortised rate is the wrong number to decide on
The figure a prepay offer prints — the lump sum divided by the term, with a “/mo” after it — describes an outcome that only exists if you complete the term. It is a forecast presented as a price. Our true-cost calculator computes it honestly and calls it what it is, an amortised rate.
What it cannot tell you is what happens if the forecast is wrong. Discontinuation on this category is high, and the reasons are ordinary: side effects, a dose change, a supply gap, a plan that starts covering it. Every one of those ends the term early, and at that moment the amortised rate stops describing anything. The relevant number becomes the one this page computes — what you have spent against what those same cycles would have cost at the rate you could have paid.
The break-even cycle is where those two cross. Before it, the prepay is a loss you are still paying off. After it, the discount is real. A term whose break-even sits near its end is a deal with very little margin for anything going wrong.
How the math works
Prepay rate per cycle = lump sum ÷ cycles covered. The rate the marketing quotes.
Break-even cycle = lump sum ÷ the no-commitment price, rounded up. It is the first cycle at which what you would otherwise have spent has caught up with what you did spend. Rounded up because a fraction of a cycle does not get you there.
Your position at any cycle = the lump sum minus the no-commitment price × cycles used. Positive means you are still behind by that much; negative means the prepay is ahead.
Saved if you finish = the no-commitment price × the full term, minus the lump sum. When that figure is negative, the prepay is not a discount at all — the calculator says so in as many words.
What this calculator does not tell you
Key terms
- Break-even cycle
- The first cycle at which the money you would have spent month-to-month has caught up with the lump sum you actually paid. Before it, the prepay is behind.
- No-commitment price
- What one cycle costs with no term attached, from the provider's own published terms. The rate a prepay is being measured against.
- Amortised rate
- A lump sum spread evenly across the cycles it covers. An honest description of a deal completed — and a forecast, not a price, until it is.
- Position
- Where you stand if you stop after a given cycle: the lump sum minus what those cycles would have cost at the no-commitment rate.
This tool performs arithmetic only. It is not financial advice and knows no specific provider's pricing or refund policy beyond what you enter. Repeat the calculation against the provider's own published terms before you commit to a plan.