Burn Rate & Cash Runway Calculator
From beginning and ending cash and the elapsed months, compute the monthly net burn and how many months the cash will last (runway).
輸入資料
計算結果
重點速覽：Burn rate measures how much net cash a pre-break-even company consumes each month and how long the cash lasts — the core survival metric for startups. net burned = beginning - ending cash; monthly burn = net burned / months; runway = ending cash / monthly burn. Example: start 500k, after 3 months 350k left → burned 150k, 50k/month; runway = 350k / 50k = 7 months. A shorter runway means raise revenue, cut cost or arrange funding. WARNING: Assumes constant burn and all ending cash usable; update monthly. This is net burn (revenue netted); gross spend is separate.
計算公式
淨燒錢總額 = 期初現金 − 期末現金。
每月燒錢率 = 淨燒錢總額 ÷ 期間月數。
資金跑道 = 期末現金 ÷ 每月燒錢率。
$$\text{Monthly Burn} = \dfrac{C_{\text{begin}} - C_{\text{end}}}{n}$$$$\text{Runway} = \dfrac{C_{\text{end}}}{\text{Monthly Burn}}$$使用說明
- Enter the cash at the start and end of the period.
- Enter the elapsed months.
- View the monthly burn and the runway in months.
以期初現金 HK$500,000、期末現金 HK$350,000 (共燒 15 萬) 為例，不同期間月數對應的每月燒錢率與資金跑道
| 期間月數 | 淨燒錢總額 | 每月燒錢率 | 資金跑道 (以期末 35 萬計) |
|---|---|---|---|
| 2 個月 | HK$150,000 | HK$75,000 | 4.67 個月 |
| 3 個月 | HK$150,000 | HK$50,000 | 7.00 個月 (本例預設) |
| 4 個月 | HK$150,000 | HK$37,500 | 9.33 個月 |
| 6 個月 | HK$150,000 | HK$25,000 | 14.00 個月 |
| 12 個月 | HK$150,000 | HK$12,500 | 28.00 個月 |
同樣是燒掉 15 萬，若這是在 2 個月內發生，每月燒 7.5 萬、跑道僅 4.67 個月 (警號);若攤在 12 個月，每月只燒 1.25 萬、跑道長達 28 個月。這說明燒錢率必須連同『期間』一起看:單看『燒了多少』不夠，關鍵是『燒得多快』與『還剩多少個月』。
理財情境案例
半年檢視：期初 120 萬、期末 90 萬、共 6 個月
某初創公司半年前手持現金 HK$1,200,000，六個月後剩 HK$900,000。淨燒錢總額 = 1,200,000 − 900,000 = HK$300,000，每月燒錢率 = 300,000 ÷ 6 = HK$50,000。
以現餘的 900,000 計，資金跑道 = 900,000 ÷ 50,000 = 18 個月。這代表若燒錢速度維持不變，公司還有約一年半的現金緩衝。18 個月的跑道相對健康 — 足夠團隊專注把產品做到有收入、或從容地籌備下一輪融資。但創業者仍應每月更新這個數字，因為一旦招聘擴張或市場推廣加碼，燒錢率會上升、跑道會縮短。管理燒錢率的核心，就是隨時知道『照現在的速度，我還剩幾個月』。(數字為便於說明的假設值。)
現金不減反增：已達正現金流
某公司季初現金 HK$300,000，三個月後不減反增至 HK$380,000。淨燒錢總額 = 300,000 − 380,000 = −HK$80,000 (負數)，即這三個月現金淨增 8 萬。
當期末現金高於期初，代表公司同期的收入已超過支出，達到『正現金流』— 不再是在燒錢，而是在累積現金。此時『資金跑道』的概念已不適用 (本工具會顯示為 0，表示並非在燒錢)，用它衡量存活已無意義。這是初創努力的目標里程碑。到了這個階段，思考的重點應從『還能撐多久』轉為『如何把盈餘善用』:建立現金儲備以抵禦波動、再投資於增長、或償還早期債務。不過仍要留意現金流的持續性 — 若正現金流只是靠一次性收入或季節性因素，仍需審慎，確認它是可持續的結構性改善。
常見問題
Is burn rate gross or net spend?
This tool uses net burn — beginning minus ending cash already nets off revenue, reflecting the true net cash consumption. For gross spend only, add revenue back to ending cash, or divide total expenses by months.
Why use ending cash for the runway?
Because ending cash is what you actually have left to burn. Divide it by the monthly burn to get roughly how many months you survive at the current pace. A runway under 6 months is usually a warning — cut spend or raise funds.
What if ending cash is higher than beginning?
Then you added cash net (reached positive cash flow); net burn is negative and the tool shows runway 0 (not burning). Then the focus shifts from survival to using the surplus — build reserves, reinvest or repay early debt.
What is the difference between gross and net burn?
Gross burn = total monthly operating expenses (payroll, rent, marketing, cloud) ignoring revenue — how much it costs to keep the lights on. Net burn = gross burn minus revenue — the actual monthly cash drop. This tool derives net burn from the cash change. Net burn links directly to runway; gross burn helps assess cost structure and worst-case (revenue = 0) survival.
How do I extend a short runway?
Three levers, often combined: (1) Cut costs — freeze non-core hiring, renegotiate rent/supplier contracts, trim weak marketing; lowers the denominator, lengthens runway. (2) Raise revenue — faster monetisation, higher pricing, deposits. (3) Fundraise — equity, loans or government SME schemes add cash. Start fundraising ~6 months before cash runs out; emergency funding is harder and cheaper when you have time.
相關工具
參考資料
內容審核：香港計算器財經團隊。燒錢率與資金跑道公式參考初創財務通用做法，並就本地創業支援情境參照香港生產力促進局及貿易發展局的中小企資訊，結果僅供教學與估算參考。