Core formulas
yearly_from_monthly = monthly_price × 12
true_monthly_from_annual = annual_prepay ÷ 12
cost_per_use = yearly_from_monthly ÷ sessions_per_year
| Display price | Annualized |
|---|---|
| $9.99/mo | $119.88/yr |
| $14.99/mo | $179.88/yr |
| $19.99/mo | $239.88/yr |
| $89/yr prepay | $7.42/mo effective |
Sort your spreadsheet by annualized descending — top three lines are usually most of spend.
“20% off annual” — real discount check
discount_truth = 1 - (annual_prepay ÷ (monthly × 12))
If discount_truth < 15% and you might churn in 6 months, stay monthly.
Per-use sanity (optional)
| Service | Annualized | Uses last 90d | Cost/use |
|---|---|---|---|
| Gym app | $240 | 4 | $60 |
| Chat AI | $240 | 90 | $2.67 |
High cost/use → cancel or downgrade before negotiating family plans.
Worked example — streaming + AI
| Line | Monthly | ×12 |
|---|---|---|
| Video A | $15.49 | $185.88 |
| Video B | $16.99 | $203.88 |
| Chat AI | $20.00 | $240.00 |
| Total | $52.48 | $629.76 |
Cutting Video B funds a full AI tool upgrade — or vice versa — but not both without behavior change.
Tie to audit workflow
- Export 90 days ( subscription audit ).
- Annualize every row.
- Apply cuts with cancel playbook.
Next: Family subscription math · How to audit every subscription on your card
