I've run the churn impact numbers on subscription models and found the results consistently more damaging than founders expect — because the compounding nature of churn makes the effect non-obvious.
Churn feels like an abstract percentage until you calculate the revenue it destroys in concrete terms. Most businesses know their churn rate. Fewer have calculated the annual MRR loss, the LTV reduction, and the compounding effect on the business over a two to three year horizon. The numbers are usually more uncomfortable than the percentage implied.
Monthly Loss
Monthly revenue churn is straightforward to calculate: multiply your current MRR by the churn rate. At £45,000 MRR and 3.5% monthly churn: £45,000 × 0.035 = £1,575 of MRR lost per month.
That figure needs context. £1,575 per month is £18,900 per year lost from your current customer base, before accounting for the cumulative effect of future churn on a reduced base, and before any growth. It represents 18,900 / 45,000 = 42% of current MRR disappearing over 12 months if no new customers are added.
More usefully, it sets the minimum acquisition target: any growth ambition requires exceeding £1,575 per month in new MRR just to maintain the current base. An acquisition target of £2,000 new MRR per month produces net growth of only £425 per month — less than 1% of the base — despite what might feel like active and successful sales activity. The churn denominator erases most of the growth numerator.
Use the Churn Impact Calculator to model this precisely. Enter your MRR, monthly churn rate, and acquisition rate, and the calculator shows net MRR growth, the compounding effect on customer base size, and what churn reduction is worth in annual revenue terms.
Long-Term Impact
The long-term revenue impact of churn is most clearly visible when modelling forward over two to three years under different churn scenarios, with the same acquisition rate applied to each.
Assume a SaaS business with £30,000 MRR, acquiring £3,000 of new MRR per month, under three churn scenarios:
- 2% monthly churn (£600/month loss): Net growth = £2,400/month. After 24 months: approximately £87,600 MRR.
- 4% monthly churn (£1,200/month loss): Net growth = £1,800/month. After 24 months: approximately £73,200 MRR.
- 6% monthly churn (£1,800/month loss): Net growth = £1,200/month. After 24 months: approximately £58,800 MRR.
Same acquisition. Same starting base. The 4-percentage-point difference in churn rate produces a £28,800 MRR difference — nearly the entire starting MRR — after just two years. In annualised revenue terms, that is a difference of over £345,000 from a single metric improving by 4 percentage points.
These figures do not compound exactly because the churn loss percentage applies to an evolving base — but the direction and magnitude are directionally accurate. The message: churn improvement does not just reduce an ongoing cost; it changes the long-term trajectory of the business in a way that acquisition investment alone cannot replicate.
Real Examples
Example 1 — Email marketing tool, high churn:
200 customers at £49/month average = £9,800 MRR. Monthly churn: 8%. Monthly loss: £784. Annual loss from existing base: £9,408 — nearly equivalent to the entire current MRR. To grow at all, this business must acquire more than £784 of new MRR per month before seeing a penny of net growth. Its acquisition economics are fundamentally impaired by the churn rate regardless of how good the product is.
Example 2 — Project management SaaS, moderate churn:
350 customers at £85/month average = £29,750 MRR. Monthly churn: 2.5%. Monthly loss: £744. Annual loss from existing base: £8,928. With £2,500/month acquisition, net growth is approximately £1,756/month — healthy and compounding. The same acquisition budget at 5% churn would produce near-zero net growth.
Example 3 — HR platform, low churn:
180 customers at £220/month = £39,600 MRR. Monthly churn: 0.8%. Monthly loss: £317. The low churn reflects enterprise characteristics — high switching costs, deep integration, long contracts. Even modest acquisition of £1,500/month new MRR produces strong net growth because the base is highly stable. This business's growth is acquisition-constrained, not churn-constrained — a fundamentally different and better problem to have.