Pay Off Debt or Invest? Compare Both Options in 2026

How the pay-off-debt-or-invest comparison is worked out

On the defaults — a $10,000.00 lump sum, an 18.00% debt APR, a 7.00% investment return, and 5 years — paying off the debt ends at $24,432.20 (interest avoided $14,432.20), investing ends at $14,176.25 (growth $4,176.25), and paying off the debt wins by $10,255.95. The whole calculation is three moves: compound the lump sum at the debt APR for the debt-side ending, compound it at the investment return for the invest-side ending, and subtract for the gap.

Five things about the model are worth stating plainly. First, the debt-side ending is the lump times (1 + APR/12) to the power of 12 × years — $10,000.00 × 1.015⁶⁰ = $24,432.20 — the interest the payment avoids over 5 years. Second, the invest-side ending is the lump times (1 + return/12) to the power of 12 × years — $10,000.00 × 1.005833⁶⁰ = $14,176.25. Third, the gap is the debt ending minus the invest ending, worked out from the unrounded endings and rounded to cents — $24,432.20 − $14,176.25 = $10,255.95. Fourth, the winner is decided from the rounded gap: a positive gap means paying off the debt wins, a negative gap means investing wins, and a rounded gap of exactly $0.00 is a Tie. And fifth, this is a simplification — it treats the debt as compounding untouched (real debts have minimum payments and the balance falls as you pay), ignores taxes, investment risk, and the fact that investing returns are never guaranteed; all listed in Accuracy & limitations.

The worked example, line by line

Setup: $10,000.00 lump sum, 18.00% debt APR, 7.00% investment return, 5 years.

Line 1 — compound the lump at the debt APR. The debt-side ending is $10,000.00 × 1.015⁶⁰ = $24,432.20 — interest avoided $14,432.20.

Line 2 — compound the lump at the investment return. The invest-side ending is $10,000.00 × 1.005833⁶⁰ = $14,176.25 — growth $4,176.25.

Line 3 — subtract for the gap. The gap is $24,432.20 − $14,176.25 = $10,255.95 — paying off the debt wins by $10,255.95.

Every branch, checked

Debt APR 8%: Lump sum $10,000.00, debt APR 8.00%, investment return 7.00%, 5 years: debt ending $14,898.46 (interest avoided $4,898.46), invest ending $14,176.25 (growth $4,176.25), gap $722.20, paying off debt wins by $722.20 — at an 8.00% APR the debt side barely beats investing: the gap is $722.20.

Invest return 12%: Lump sum $10,000.00, debt APR 18.00%, investment return 12.00%, 5 years: debt ending $24,432.20 (interest avoided $14,432.20), invest ending $18,166.97 (growth $8,166.97), gap $6,265.23, paying off debt wins by $6,265.23 — a 12.00% return narrows the gap to $6,265.23, but the debt still wins.

Invest return 20%: Lump sum $10,000.00, debt APR 18.00%, investment return 20.00%, 5 years: debt ending $24,432.20 (interest avoided $14,432.20), invest ending $26,959.70 (growth $16,959.70), gap $2,527.50, investing wins by $2,527.50 — the flip: only a 20.00% return beats an 18.00% APR, and investing wins by $2,527.50.

Horizon 10 years: Lump sum $10,000.00, debt APR 18.00%, investment return 7.00%, 10 years: debt ending $59,693.23 (interest avoided $49,693.23), invest ending $20,096.61 (growth $10,096.61), gap $39,596.61, paying off debt wins by $39,596.61 — ten years nearly quadruples the gap to $39,596.61.

Lump sum $25,000: Lump sum $25,000.00, debt APR 18.00%, investment return 7.00%, 5 years: debt ending $61,080.49 (interest avoided $36,080.49), invest ending $35,440.63 (growth $10,440.63), gap $25,639.86, paying off debt wins by $25,639.86 — two and a half times the lump, two and a half times the gap: $25,639.86.

Debt APR 24%: Lump sum $10,000.00, debt APR 24.00%, investment return 7.00%, 5 years: debt ending $32,810.31 (interest avoided $22,810.31), invest ending $14,176.25 (growth $4,176.25), gap $18,634.06, paying off debt wins by $18,634.06 — a 24.00% APR widens the gap to $18,634.06.

Horizon 2 years: Lump sum $10,000.00, debt APR 18.00%, investment return 7.00%, 2 years: debt ending $14,295.03 (interest avoided $4,295.03), invest ending $11,498.06 (growth $1,498.06), gap $2,796.97, paying off debt wins by $2,796.97 — two years is not enough time for the APR to dominate: the gap is $2,796.97.

The reverses, worked backwards

Lump sum for a $5,000.00 gap: $4,875.22 — the exact lump sum is 4875.2211. At the displayed $4,875.22 the gap is $5,000.00 (exact to the cent). $4,874.22 gives a $4,998.97 gap; $4,876.22 gives a $5,001.02 gap. The star is DOLLARS.

Investment return for an exact tie: 18.00% — the exact return is 18.0000%. At 18.00% both sides end at $24,432.20 and the gap is $0.00 (exact tie). At 17.99% paying off debt wins by $12.03; at 18.01% investing wins by $12.04. The star is a PERCENT.

Horizon for the gap to reach $10,000: 5 years — the smallest whole number of years at which the gap reaches $10,000. At 5 years the gap is $10,255.95; 4 years gives $7,214.24. This is a step reverse: the horizon comes in whole years here, so there is no exact in-between. The star is YEARS.

Debt APR for a $5,000.00 gap: 13.09% — the exact APR is 13.0927%. At the displayed 13.09% the gap is $4,997.48, $2.52 under the $5,000.00 target — rounding. 13.08% gives $4,988.00. The star is a PERCENT.

Investment return for a $1,000.00 gap: 17.15% — the exact return is 17.1519%. At the displayed 17.15% the gap is $1,002.24, $2.24 over the $1,000.00 target — rounding. 17.16% gives $990.69. The star is a PERCENT.

Lump sum for a $20,000.00 investment ending: $14,108.10 — the exact lump sum is 14108.1008. At the displayed $14,108.10 the invest ending is $20,000.00 (exact to the cent). $14,107.10 gives a $19,998.58 invest ending; $14,109.10 gives a $20,001.42 invest ending. The star is DOLLARS.

What the defaults assume

The defaults are a $10,000.00 lump sum, an 18.00% debt APR, a 7.00% investment return, and 5 years — debt ending $24,432.20, invest ending $14,176.25, gap $10,255.95, paying off debt wins by $10,255.95. With a horizon of 0 years, Lump sum $10,000.00, debt APR 18.00%, investment return 7.00%, 0 years: debt ending $10,000.00 (interest avoided $0.00), invest ending $10,000.00 (growth $0.00), gap $0.00, Tie — no time, no difference, a Tie. With a lump sum of $0, Lump sum $0.00, debt APR 18.00%, investment return 7.00%, 5 years: debt ending $0.00 (interest avoided $0.00), invest ending $0.00 (growth $0.00), gap $0.00, Tie — nothing to put anywhere, a Tie. With a debt APR of 0%, Lump sum $10,000.00, debt APR 0.00%, investment return 7.00%, 5 years: debt ending $10,000.00 (interest avoided $0.00), invest ending $14,176.25 (growth $4,176.25), gap $4,176.25, investing wins by $4,176.25 — the debt side stays at $10,000.00 and investing wins by $4,176.25. With an investment return of 0%, Lump sum $10,000.00, debt APR 18.00%, investment return 0.00%, 5 years: debt ending $24,432.20 (interest avoided $14,432.20), invest ending $10,000.00 (growth $0.00), gap $14,432.20, paying off debt wins by $14,432.20 — the invest side stays at $10,000.00 and the debt wins by $14,432.20. With a horizon of 30 years, Lump sum $10,000.00, debt APR 18.00%, investment return 7.00%, 30 years: debt ending $2,127,037.81 (interest avoided $2,117,037.81), invest ending $81,164.97 (growth $71,164.97), gap $2,045,872.83, paying off debt wins by $2,045,872.83 — the 30-year debt figure assumes the balance compounds untouched, a simplification. With a lump sum of $1,000,000.00, Lump sum $1,000,000.00, debt APR 18.00%, investment return 7.00%, 5 years: debt ending $2,443,219.78 (interest avoided $1,443,219.78), invest ending $1,417,625.26 (growth $417,625.26), gap $1,025,594.52, paying off debt wins by $1,025,594.52.

Output · formula · meaning

Who uses this

• The borrower with an 18% card: they learn paying it off wins by $10,255.95 — and they check the $4,875.22 reverse to see the lump at which the gap first reaches $5,000.
• The borrower with an 8% loan: they learn the gap shrinks to $722.20 — and they check the 18.00% reverse to see the return that ties the debt.
• The investor expecting 20%: they learn investing wins by $2,527.50 — and they check the 17.15% reverse to see the return that leaves a $1,000.00 gap.
• The borrower with 10 years: they learn the gap is $39,596.61 — and they check the 5-year step to see when the gap first reaches $10,000.

Accuracy & limitations

The math is first-principles: each ending is the lump sum times (1 + rate/12) to the power of 12 × years; the gap is the unrounded debt ending minus the unrounded invest ending, rounded to cents half-up; the winner is decided from the rounded gap, and a rounded gap of exactly $0.00 is a Tie. What the model cannot do is tell you what YOUR debt or investment will do: it is a simplification only — it does NOT model minimum payments, so it treats the debt as compounding untouched while a real balance falls as you pay; it does NOT model taxes on investment gains or any interest deduction; it does NOT model investment risk, fees, or the fact that returns are never guaranteed; and it assumes the APR and the return stay flat for the whole horizon, while both move. An 18% APR beats a 7% return by $10,255.95 over 5 years — but the return gap between any real debt and any real investment in any real 5 years can dwarf the model either way. Use it to see the trade-off, then check the debt’s actual rate and the investment’s actual risk before you choose.

Frequently asked questions