A payment model, not a lending quote
CalcFlow estimates a fully amortising loan with equal monthly payments, a constant nominal annual interest rate and payments at the end of each month. Enter the amount borrowed, annual interest percentage and a whole number of months. The tool shows monthly payment, total repayment and total interest.
It does not check eligibility, compare lenders or include arrangement fees. The annual rate input is not automatically equivalent to a regulated annual percentage rate that incorporates fees or different compounding conventions. Use the rate and repayment structure in an actual agreement when comparing the estimate with an offer.
How the repayment is calculated
Let P be principal, r be the annual rate divided by 100 and then by 12, and n be the number of monthly payments. The formula is payment = P × r ÷ [1 − (1 + r)−n]. At a zero interest rate, the payment is simply P divided by n.
Each payment covers interest on the outstanding balance and a portion of principal. Early payments generally contain more interest because the balance is larger. As principal falls, the interest component falls and more of the same payment repays the original borrowing.
Total repayment is the unrounded calculated payment multiplied by the number of months. Total interest is that total minus principal. Actual schedules may adjust the final instalment because of cent-level rounding or use daily interest conventions that differ from this monthly model.
Compare term length with total cost
A longer term usually lowers the monthly payment for the same principal and positive rate, which can ease short-term cash pressure. The trade-off is generally more total interest. A shorter term accelerates repayment but leaves less monthly room for inventory, payroll and unexpected expenses.
Compare scenarios using the same borrowed amount and fee assumptions. Then test whether the business can still meet payments in a slower sales month. Variable rates, payment holidays, balloon balances, early repayment charges and interest-only periods require a more detailed schedule than this calculator provides.
Break-even starts with contribution
Contribution per unit is selling price minus variable cost per unit. Variable costs are those that change with sales volume, such as materials, transaction charges and per-order packaging. Fixed costs belong to the period you are analysing, such as monthly rent or a fixed software subscription.
The formula is break-even units = fixed costs ÷ contribution per unit. Suppose illustrative monthly fixed costs are 3,000, selling price is 50 and variable cost is 30. Contribution is 20, so break-even is 150 units. At that volume, contribution covers the stated fixed costs but leaves no operating profit under the model.
CalcFlow rounds the required volume up to whole units. If price is equal to or below variable cost, it reports that there is no finite operating break-even under those assumptions. Selling more cannot cover positive fixed costs when each unit contributes nothing or creates a loss.
Keep accounting profit separate from cash flow
Loan principal repayments are cash outflows, but they are not normally operating expenses in a profit calculation. Interest and depreciation may receive different accounting treatment. Do not silently add an entire repayment to accounting fixed costs and call the answer standard operating break-even.
You can create a separate cash-coverage scenario by including the relevant scheduled cash commitments. Label it clearly and avoid counting the same cost twice. Customer payment delays, inventory purchased before sale and tax settlement dates can create cash shortages even when the operating model shows a profit.
Stress-test the assumptions
Save separate cases for a higher variable cost, a lower selling price and a larger fixed-cost base. Compare the required sales volume with realistic capacity, not just ambition. If reaching break-even requires an additional employee or machine, fixed costs may rise in steps rather than remain constant.
For multiple products, calculate a weighted contribution using an explicit sales mix, or model each product separately before combining results. A single average is convenient but can conceal a shift toward lower-margin items. Use the calculators as an initial decision screen, then build a dated cash-flow plan for a material borrowing commitment.